I have an m-audio fast track pro. It works (using the basic snd_usb_audio driver), but only one program can send audio out at one point in time. If I try to play audio from anything other than one program, I start getting access denied messages, like the following I get from mplayer:
[AO_ALSA] alsa-lib: pcm_hw.c:1132:(snd_pcm_hw_open) open /dev/snd/pcmC0D0p failed: Device or resource busy
[AO_ALSA] Playback open error: Device or resource busy
Could not open/initialize audio device -> no sound.
I'm not sure what other information is required, since it works, so I'll gladly post other stuff if requested.
It's just annoying to have one program lock the sound thingy...