Disable a linux sound card

Perhaps your NVIDIA card is set as the default audio device; I have a similar issue when trying to get audio via HDMI in e.g. Flash. Problem is my Realtek card is set as default and some applications doesn't let you select which sound device to use. I solve the issue by setting my HDMI audio as default aduio device, which can be achieved by editing the .asoundrc file in your home directory.

Here's what to do. First you have to find the proper card and device you want to use. Run the command aplay -l. I'm guessing you want audio to come out your USB headphones? From the output of aplay -l you can see that the USB headphones is card number 2 and device number 0, so put the following in your .asoundrc file.

pcm.!default {
type hw
card 2
device 0
}

ctl.!default {
type hw
card 2
device 0
}