Ok, got replay running. Little howto (for kp49):

Packages installed: alsa-utils,mplayer (all on maemo, not Easy Debian). Tested with Yamaha MW10c USB mixer.

first, connect device (standard usb audio device), start h-e-n, enable fullspeed, Vbus boost on, enumerate. Then, start an x-term and load the kernel module (probably not necessary, seems to be loaded by default):

check if your new audio device has appeared:

playing music with mplayer:

Plays perfectly, but CPU load is higher (40-50% compared to 15% when playing with mplayer through the internal DAC)

recording with arecord 44.1khz 16-bit stereo wav:

(default is the name on my n900 for the usb device, check /proc/asound/cards if it's the same for you)
I got sometimes some overruns with arecord, maybe one can change the buffer size or something similar. Hope to get a workaround... apart from that it's nearly perfect.

Next step would be to reroute the standard output to the USB if someone's interested - should be possible with pulse-audio somehow, but I have no idea about that

Oh - and anyone's got an idea for a lightweight multi-track recorder?