You could try looking for any mixer devices that you do have, and symlinking to it.
find /dev/ -name *mixer*
ln -s /dev/currentmixer /dev/sound/mixer
What motherboard are you using? I've been fighting tooth and nail to get 5.1 audio out of the A7N266-VM. ALSA 0.94, nvaudio.o, both work fine in analog but no IEC958 mixer control in alsamixer, and I haven't figured out how to get AC3 playback with an OSS module like nvaudio.o. Any hints on how to do this with mplayer? My next step is to check out the ALSA CVS and see if any progress has been made on nForce2 SPDIF.