This is the method I used to change from nf4 mainboard integrated audio to Live Value soundcard but I think it should work with any combination of soundcards. If it doesn’t leave a comment and I’ll change this text.

In terminal (Alt+F2 -> gnome-terminal) type:

sudo asoundconf list

This will list sound cards you have in your computer.

To switch to another card type:

sudo asoundconf set-default-card CARDNAME

Where CARDNAME is the name of sound card you wish to use.