Basic Problem: mpd can't set the sound volume
Hardware:  Netgear WGT634U, C-Media "3D Sound" USB adapter
Software:  Kamikaze 7.09, with these packages:
kmod-usb-core
kmod-usb2
kmod-sound-core
kmod-usb-audio
kmod-usb-ohci
kmod-usb-uhci
alsa-lib
alsa-utils
mpd

- mpd successfully plays audio files, using /dev/dsp
- mpd uses /dev/mixer to control the volume, but the output does not change
- alsamixer successfully controls the volume settings, using /dev/snd/controlC0
(strace and lsof are wonderful tools!)

The ALSA Wiki page Mapping oss mixer controls to alsa mixer shows how to set values in /proc/asound/card0/oss_mixer but that fails:

# echo 'VOLUME "Master" 0' > /proc/asound/card0/oss_mixer
# cat /proc/asound/card0/oss_mixer | grep VOLUME
VOLUME "" 0

Is the problem in /usr/share/alsa/alsa.conf file? I haven't changed anything there.  Is it in the snd_mixer_oss module? If so... what? Some compile-time setting or something? At this point, I'm a bit lost.