I had mpd running happily and listing my directory of music, but I couldn’t get any output from the hardware. After spending a few hours chasing my tail I thought I’d leave a note of my steps:
Follow the guide here
and be sure to
sudo adduser $USER audio
then Tone1 will show up when you use
aplay -L and mpd can output audio. The
audio group comes from the mpd.conf defined in the linked tutorial.