I had go through some pain and suffering to get USB audio to work on my Asus WL-500gp V2, so I thought I'd share. Particularly, I had to get some components from OpenWRT and edit the binary files so that they'd point to a different uGlibc; some of the symbols I needed were missing.

Anyway, here's a squashfs image that you can tftp up. It works with a CMedia USB audio adapter. If you get it working, you can do this: 

wget -O - http://maddie.brainhat.com:8000/ices.m3u | madplay -

Image: test30.trx

You can take the image apart with the firmware mod kit on the DD-wrt site if you need to modify it.