I've been wanting to try using my n800 with a usb-audio device for a while now, my Etymotic earbuds just don't sound very good with the n800 unless I use an amp...

Anyway, I was eventually able to get usb-audio working, but it wasn't easy, at least for me. (I used an Xitel HiFi Link AN1 for testing.)

I had to build the usb audio kernel modules and copy over some of the other alsa modules:

snd-rawmidi.ko, snd-usb-lib.ko, snd-hwdep.ko, snd-page-alloc.ko, snd-timer.ko, snd-pcm.ko, snd-usb-audio.ko

This got me to the point where I could see usb audio card in /proc/asound, but I was unable to play any music through it.

I ended up having to compile the latest versions of alsa-lib and alsa-plugins to get things working. In the process I managed to make my flash-card install unbootable for a while, by not completely replacing the old libraries... The watchdog thingie will reboot the device if multimediad crashes.

Now I can send music to the usb device with:
mplayer -ao alsa:device=hw=1.0 music.wav

I haven't tried getting this to work with any other media players yet.

So it works, but it's not very easy to get working. I don't have a debian installation for my n800 yet, but I imagine this would be a much easier way to go.