open a terminal on your core and type:
sudo ssh moon## (replace the ## with the device number of the MD)
it will ask for your password put it in then it will say-
From there just type
When that opens use the arrow keys to turn the volume up on all the outputs listed. If you see "mm" at the bottom of any of the outputs highlight it and hit the "m" key on your keyboard to unmute it then turn it up. Hit esc when you are done to save your values.
If that doesnt work, I would delete the MD from the web admin and recreate it.