2014 S60 no audio at all, but a power up pop

[azureblue]

Trying to help out a friend here - There is no audio from the speakers. He has been to the dealer, a well qualified car audio shop, and an indy Volvo mechanic. (Since friend is no mechanically tilted, I am sure he missed some of what they were telling him) Connections have been tested all the way back to the amp, fuse checked. It powers on, but all you hear is a quiet "pop" when the radio / head unit comes on. No audio from the rest of the car's sound system, either.
So, #1 - does anyone have an idea what it could be?
#2 - if the head unit is dead, can I swap out with a parts yard unit? And if so, what year range? Much thanks