Does the student have a cell phone? They could host the zoom call on the cell, and use the computer to run band in the box. To mix the analog signals the student could pick up a small mixer. There are some really low cost options out there.
Cheap as they come

or you can get a more robust small format mixer:
Mackie 402

I'm sure he has a cell phone, but that wouldn't be ideal because the screen size is super small, not effective for watching the teacher.
I wonder if perhaps he could use two sound cards at the same time in his laptop? The built in one, and add a USB sound card. Send Zoom speaker to one, and send the BIAB audio to the one that is connected to the mixer, is that possible?

I think you are correct in wanting to keep the band audio and the Zoom replay audio separate. To do this means adding a device that appears to applications as a separate audio output, and then this can be used for either of the two sources - it's probably easier to route the Zoom output that way. Doing this would give him the two domestic line-level audio sources plus the microphone to feed into the mixer, as you have in your setup.

As to what device you could use for this, then almost anything with a USB input and either a headphone jack or a pair of RCA (EU=phono) output, as the quality reconstructed from a Zoom call is not great. This sort of device is very cheap on Ebay. Links get automatically deleted if I put them here, but I get several hits if I search Ebay.co.uk for "USB External Stereo Sound Card" or "USB to 3.5mm mic headphone jack"

In looking at the settings in BIAB, I think that should be possible as the audio drivers setup allows you to choose the output. I have a USB sound card on my other computer, so I can easily test the setup by adding it to my laptop and see if it shows up.

But I just thought of another problem. In addition to the student hearing the other end of the Zoom call, he needs to hear his own guitar and backing track. If the audio from BIAB, and his guitar are going into the mixer, and the mixer goes into the computer, then he won't hear himself where he is. So I guess he also will need to get some speakers to use as monitors.

This is where you have to choose the capabilities of the type of mixer you require. A mixer that has at least one Aux output that all the channels can feed via their separate (rotary) faders would give you a sub-mix that could be sent to the Zoom input. The headphone output would have the full mix that includes the incoming Zoom audio.

If the mixer had the capability of headphone monitoring of Aux outputs, you could use the main mix outputs for the sub-mix, and also cable them back to a spare input pair of channels that output only to the Aux. To this Aux mix you add the audio from the Zoom session so you hear that on the phones as well as the main mix. This avoids having to do a parallel mix of the band and vocal inputs on the main and Aux faders.

I totally got lost in your reply.....Are you saying that he can take the output from the Zoom speaker, and also feed it into the mixer, so he can hear everything in his headphones? Headphones would probably be a good idea for him because it's night time during our daytime when he takes his lesson, and his family is sleeping.. Other thing is, he doesn't need to hear his own voice on the call, so there would need to be a way to keep that from happening.

I'm chatting with support online at Thomann, they're suggesting this, but I think it has more channels than necessary.
https://www.thomann.de/de/behringer_xenyx_x1204_usb.htm
Behringer Xenyx X1204 USB

Can this one do everything we need?

Behringer Xenyx QX1002 USB
https://www.thomann.de/de/behringer_xenyx_qx1002_usb.htm

I think Alesis and Yamaha are better brands from what I'm told...

It's hard to say what "better" means in this context. If a mediocre mixer does what you want, is that better than one that has higher sound quality but falls short in functionality?

That QX1002USB is reasonable value, but the headphone output can only be either the main mix or the solo bus output. You don't
seem to be able to output either of the two Aux sends to headphones. It also has the almost unusable function of the USB return replacing the main mix outputs rather than coming in as a stereo channel into the main mix.

The Allen & Heath ZEDi 10FX is a much higher-quality mixer, allows the USB returns to come in as stereo channels into the mix, and has switching of the headphones from main out to the Aux send.

Allen & Heath ZEDi 10FX

This pluggin might do the trick. Its essentially a "vritual mixer". I bought it to run pluggins on my daily computer to control volume differnces within youtube, and to eq things.

I haven't used it yet, but it says it can route audio from one app to another.

https://ddmf.eu/virtual-audio-stream/

I sketched out what I think needs to be achieved as follows (probably should have done this before)

1. Guitar INTO Mixer
2. Microphone INTO Mixer
3. Laptop internal soundcard OUT sends Band in a Box audio INTO Mixer
4. Laptop usb soundcard OUT sends Zoom "speaker" INTO Mixer

5. Mixer USB out sends Guitar, Microphone, Band in a Box to Laptop/Zoom "microphone" setting which goes to the other caller.
6. Mixer Headphone out sends Guitar, Band in a Box, and Zoom speaker (from other end of the call) into Headphones
   Does this all sound right? And if so, what would be the least expensive mixer that can achieve it, available at Thomann?

MC208, post: 468211, member: 49667 wrote:
I sketched out what I think needs to be achieved as follows (probably should have done this before)

1. Guitar INTO Mixer
2. Microphone INTO Mixer
3. Laptop internal soundcard OUT sends Band in a Box audio INTO Mixer
4. Laptop usb soundcard OUT sends Zoom "speaker" INTO Mixer

5. Mixer USB out sends Guitar, Microphone, Band in a Box to Laptop/Zoom "microphone" setting which goes to the other caller.
6. Mixer Headphone out sends Guitar, Band in a Box, and Zoom speaker (from other end of the call) into Headphones
   Does this all sound right? And if so, what would be the least expensive mixer that can achieve it, available at Thomann?

The Allen & Heath ZEDi 10FX does all that. It could be that it would in addition not require the external USB sound card, as the mixer can receive two stereo channels via USB, and send two channels to the computer via USB, but you would have to check this.

There's also a ZEDi-8; would that work as well, or the ZEDi 10FX would be the minimum to meet the requirements?
He's even less technical as me, so I figured a USB sound card would be easier than getting into manipulating channels and all that...

Your going to want to find a unit that does it all, because the onboard soundcard will have very high latency and even if you aggregate two "soundcards" ie interfaces, the latency will be at the mercy of the slowest device, the onboard soundcard.

Yamaha makes an affordable mixer with a guitar amp sim dsp, and its a USB mixer. Its got loopback functionality which is aimed at podcasters who need to play audio from sources in the computer. They cite online lessons as a use in the promo material

https://usa.yamaha.com/products/music_production/interfaces/ag_series/index.html

The pluggin i linked would should be able to route audio from band in a box, and send it to zoom a long with the mic and guitar. This way Your not syncing two soundcards/ interfaces. It might not be necessary w the Yamaha, but would allow a choice of any interface.

I had not even considered latency as being an issue :-( The Yamaha mixer looks interesting, I'll have to read more about it. Would the smaller AG03 be good?

As far as the plugin, I don't understand what it does? The description on the website doesn't make any sense to me? Would he need that plugin if he has the AG mixer?

Is this the part you're referring to about using this mixer for Zoom?:

Attached files

MC208, post: 468218, member: 49667 wrote:
I had not even considered latency as being an issue :-( The Yamaha mixer looks interesting, I'll have to read more about it. Would the smaller AG03 be good?

Its been a while since i compared the 2 models. Off memory the ag03 has channels, so he could do guitar, mic, and phone/ tablet ect. It seems to meet the bare minimum requirements, but max out there too, so no room for expansion.

Id have to look at them again to do a real cost v benefit anylisis. The extra preamp on the other model could be handy if he wants to mic an amp instead of use the guitar amp sim dsp.

MC208, post: 468218, member: 49667 wrote:
As far as the plugin, I don't understand what it does? The description on the website doesn't make any sense to me? Would he need that plugin if he has the AG mixer?

The pluggin is like a virtual mixer inside the computer. So you can take audio from different apps and route them as needed. Example route pandora, band in a box, and youtube, all to zoom. Or Send the audio from those apps to one main output like headphones, and control there volumes within the pluggin. Or send the zoom lesson to a recording program. Or if he were using a guitar rig standalone pluggin for guitar amp sim, he could send that to zoom. It just allows you to route signals from one program to another.

I would verify with ddmf if it works with the software you are intending to use it with.

If it works as described it should fit the bill. Im in an interim here so my stuff is all boxed and i haven't used the pluggin yet.

He wouldn't need the pluggin with the AG, if the AG loopback could handle the band in a box, and then the mixers signals all feed zoom.

Again i hate to be vague here, but i am limited in what i can do right now. Appologies.

A sales person, or Yamaha rep, should be able to confirm it will do what you need without the additional pluggin.

MC208, post: 468218, member: 49667 wrote:
Is this the part you're referring to about using this mixer for Zoom?:

Yes that was the part that caught my eye. Between loopback, and dsp guitar sim, its feature set seemed to fit his needs nicely.

I should note that some interfaces now feature loopback since podcasting is popular. I think focusrite scarletts do among others.

https://www.soundonsound.com/reviews/yamaha-ag06-ag03

There is a decent write up.

Imho the 06 would be the way to go. For the extra 50$ you get more inputs, the amp sim, effects on 2 channels, and another pre amp.

At one point i read the manuals to look at the exact differences particularly with the effects sections. But to me the ag06 is a better overall value.

I just found out from him that it's a work laptop and he might not even be allowed to install BIAB on it.. I chatted with tech support at Yamaha, didn't find it very helpful. If he does get BIAB, I guess he might just have to render his tracks to audio and play them from his phone or something into the mixer. I still don't understand what loopback does despite the diagrams and what I've read. How is it different from any other mixer? It takes the inputs from the channels and sends them out via the USB to the computer, same thing my ZED10FX does as far as I can tell.

Dissapointing yamaha support couldn't be more helpful.

Its probably possible to install biab to an external ssd so its not installed on the PC itself.

From the focusrite website:

"On supported Scarlett 3rd gens we have included Loopback. Focusrite Control’s Loopback feature lets you record other audio sources from within your computer (e.g., the audio output from a web browser). Loopback uses the Scarlett’s 'virtual' inputs, which have no physical connectors on the hardware interface itself but may be selected in the DAW as signal sources for recording in the same way as any other."

Thus, by selecting the Loopback output as the recording source on a mono or stereo DAW track, you can record from another software application into your DAW. Note that your computer will assign DAW 1 and DAW 2 as the default sound output channels."

It allows you to blend audio sources that are generated in a program on the pc, with inputs from the mixer, and send them all to the same destination ie a streaming or recording app.

It keeps things lined up and avoids extra analog to digital conversions.

--

Typically something like the zed or another interface that doesn't have loopback, wouldn't accept audio from biab and send it to another program. It would only accept audio to/from a single program, not 2 at a time. All the ins/outs would be from the mixer itself. The interface would only "see" one program at a time.

--

You can try and see if the zed has this function, it depends on the audio drivers.

MC208, post: 468216, member: 49667 wrote:
There's also a ZEDi-8; would that work as well, or the ZEDi 10FX would be the minimum to meet the requirements?
He's even less technical as me, so I figured a USB sound card would be easier than getting into manipulating channels and all that...

Sorry, I somehow missed seeing this question earlier. The ZEDi-8 is unfortunately too stripped down for this application, but the ZED-10 (without the FX effects) has the 4-in and 4-out USB capability and should work just fine.

This ZED-I series of small USB mixers are a crossover between an audio interface and a stand-alone mixer. Once you have a simple picture in your mind of what sounds are coming from where, they are intuitive to operate.

It's way too complicated for me, let alone this guy in Europe I'm trying to help, who is even less techy than me. I may go ahead and recommend him the Yamaha mixer as it looks like a good piece of equipment, and not costly. But I might just tell him to play MP3 tracks from his phone or other audio player into the mixer; i.e. make up the track in band in a box, and render it out to a wav format.