How about.. good luck?
FreeNAS has no support for audio, at all. You'd have to add it yourself. You can request it be added via a ticket, but don't count on it being added anytime soon unless you are providing the source code. Even then, it may not be added to the trunk because your typical FreeNAS server isn't intended to be used as a jukebox. You could easily use a phone and just access the shares on the phone and plug speakers into the phone's audio output.