I have an internal soundcard and an external USB soundcard that I use because the headphone jack in my laptop is broken. I need to be able to disable the internal card so sound will go through the USB card. This was acheivable through system settings > sound in 11.10 .
I tried clicking on the internal sound card in the list, and muting it, then going to the USB sound card's digital output (S/PDIF) and found that it was muted as well, so I unmuted it. Then, I hit test sound, but the sound came through internal speakers again. I checked the internal card, and it was unmuted again.
I repeated the same process with the analog output of the USB card as well. Same thing happened.
I have not tried this yet, but I believe when I plug in my Logitech webcam, I will need to disable the built-in laptop microphone, the laptop mic jack, and the USB mic jack, for the microphone in the webcam to work as well.
The input side is suffering the same problem as output about muting all devices instead of just one. Maybe I'm missing something on the dialog.
I just need to know how to selectively enable/disable sound devices through the options dialog. I'm sorry if I put this in the wrong place, probably need to file bug report.