OK so I got an aftermarket headunit with nav etx, everything is cconnected (went to a reputable audio shop) and now the rear speakers aren't working. I have to bring it back to them but they have no clue what's going on. Anyone have any insight?

 

Not sure (however I did find a similar thread) on a honda ( Rear speakers appear to of stopped working - Honda-Tech ). Since I havent pulled mine apart yet.

 

but they're reputable... why can't they figure it out

 

They probably have the unit connected wrong. There will be a radio harness that needs to be connected properly. Assuming they didn't run new wires to put all the speakers on an amplifier.