I had a similar problem with vortexbox and alsa audio output several years ago. Caused by the the alsamixer default the output to 00.
Solution then was to go to 'alsamixer' and increase the level manually from the CLI GUI.
Alsamixer isnt installed, from what I can see as I'm sure things have changed. Looks like pulseaudio is now used.
I don't really know what I'm talking about, but thought it might help someone to look in the right direction.