I am not sure if it is true for all USB sound cards. I have a Sabrent (USB-SBCV), I think i purchased from amazon.com
With it, I find I need to set it up to be the default PCM sound device (Had to do the same on other machines as well)
I had to create a file: /etc/asound.conf
with the contents:
pcm.!default sysdefault:DeviceDon't remember if I had to reboot after I created this or not, but I did when I first installed it on my Edison.
Kurt