Mac or Windows? A limited version of what you are talking about is possible under the Mac OS's Device Aggregation scheme, where it presents a unified interface to the DAW, but comes at a (slight) performance cost. No such scheme exists natively under Windows, but some software interfaces such as the various incarnations of ASIO allow a degree of device independence.

daisy chaining same devices is common.
ive never heard someone trying to connect different devices unless you were attempting to use one in "standalone mixer mode" and cheated the main outs for use as a summing bus.
i dont think youd ever be able to select the multiple asio drivers in your daw

I'm not aware of it being able to be done, at least not successfully. While I can't say that it's 100% impossible... I can say that I've never seen anyone do it on a PC.

I do know that most every audio I/O glitch I've ever seen involving multiple audio I/O devices - where one is a "stock" resident PC card - like a Realtek or Soundblaster - when integrated with a USB audio device, are generally fixed pretty fast when you disable the cheap internal card in your OS.

As far as I'm aware, in windows, you have to choose which I/O is your default, and accordingly, your DAW will only recognize that one which is active.

You can have multiple I/O's using different I/O devices chained together, as Josh mentioned... so you could have something, like say a Presonus 1818VSL and a Focusrite OctoPre, as both have optical connections, at which point, one device becomes the master, the other a slave, but there's still only one USB/FW connection to the PC, so the computer still only sees one default audio device resident, but at least with this method, your DAW can see the two different devices that chained together, ( or at least all DAW's I'm aware of can ) at which point you can then choose either device and its corresponding inputs and outputs in your track I/O menu.

FWIW

Thank you for your responses. It's as I thought. I mucked around with the settings (windows and application) and was able to get all of the drivers to show up in Sonar's preferences. However, I don't think Sonar cared what I was doing regarding the choices I made (Playback - Delta Out 1/2 & Record - Alpha In 1). No sound output. I restored all settings to the Alpha. The 44 was more practical when I had a slightly different setup years back. I just wanted to make sure that this sort of dual setup might have possibilities (for me). Thanks again, but I think it's more trouble than its worth. If I need more ins/outs in the future, I'll upgrade the Alpha.