Well you probably can. Just edit mpd.conf as follows:

audio_output {
type "alsa"
name "Usb Dac"
device "hw:0,0" # optional
# format "44100:16:2" # optional
mixer_device "hw:0" # optional
mixer_control "DIYINHK Clock Selector" # optional
mixer_index "1" # optional

Replace mixer_control with the name you see on the volume bar on alsamixer

you can find out by doing

sudo alsamixer

Restart mpd and let me know!