Had the OEM radio in a 2008 c4 replaced with an alpine nav unit. now the rear speakers don't work. Anyone know a solution for this

 

Try taking it back to whoever did the work?

 

Under the front boot is the amp, check the hookup there. My factory amp failed in similar way, started with static then rear speakers went out.

 

Do you have the 12 speaker Bose system?

 

yes. 12 speaker bose system.
I would take it back to installer, but it is 70 miles away. besides, when they installed it, it took them 10 hours. they obviously didn't know much about Porsche radio systems.

 

Your going to need to take it back. The MOST HUR (Bose) connection requires that the fader be set before you take out the factory stereo - the aftermarket radios cannot adjust front/rear fade on the Bose system - it is fixed at the volume you set it at before removing the head unit.