For anyone that's interested, I got USB audio working on the latest RootBox nightly (4/28). The support for it is a little rough but it works.
To get it working follow these steps:
1. Flash the latest nightly (4/28) if you haven't already.
2. Run the jacknorris USB Audio mod; follow the directions here: http://forum.xda-developers.com/show....php?t=2029728
3. You should now be able to output audio through USB however, if you don't do it correctly the phone will freeze.
4. To get the phone to properly output to a USB audio device you must already have an audio source playing when you connect the USB device. I use Spotify to play my music and to get the output to work I have to have music already playing through the speaker when I connect my USB DAC.
If you follow those steps you should be all set. All I know is I'm happy I finally got this working.