The Presonus Bluetube specifically is probably better than the US144. Tascam preamps are not particularly good. That said, you can't bypass the preamp in a cheap interface or cheap mixer. If they are two stage circuits sometimes you get to skip the second stage of amplification but you are still going through most of the cheap Tascam circuit.

Thanks for the really speedy reply.

I see, so it's definitely worth hanging on to anyway. The Tascam is definitely a budget interface, but that's why I got it. I was previously going from the BlueTube to an old Sound Blaster Audigy 2 NX external soundcard I had that just died. It was around $300 back in the day, but definitely for home listening and not necessarily recording, so I'd like to think the Tascam will preform better.

I have seen fairly good results with the Tascam 144. I know a person who mixes down on a Mackie 1604 and ties the stereo out to a Tascam 144. ( effectively using the 144 as an A/D converter )
As i undertand it, stereo signal goes from the 144 via USB into the computer. this particular person was using cubase to make the .wav files on the computer.
Cubase handled the USB connection with no trouble.
It has sounded pretty good for the price point. Also, I honestly dont think there is need to worry about whether the mic amp shares circuits with the line in. If you want to use your other gadget, (blue tooth or whatever it was) you should do it.
thats my $0.02 --