I don't think you'll lose your Rear AC. The Acadia has a separate AC module below the NAV. Unless you plan on removing those connections, I don't see how you could lose Rear AC control. All the controls you are talking about are audio/video based which are NAV controlled.
I have the same unit, but didn't have a problem with the rear audio level. I have the factory Bose amps/speakers - I don't know if that makes a difference. You've probably already checked your connections and tried adjusting the fader control on the AVIC?
no i actually haven't gotten around to checking the connection, i find that when i hit bumps all the speakers work. i have the bose system too. i was just gonna check the connection when i add some screens. does your setup allow u to do anything with the rear audio(ac controls) switches?
Not a good sign. Do you know what method was used to connect the speakers or head unit?
1) New wiring to each one,
2) Adapters to the factory connectors,
3) (probable) Factory wire cut or tapped and crimp connector to speaker terminal/factory wire or fold over (Scotchlok) connector to factory harness.
Many installers use the fold over type to connect to factory wires and most of the time they work OK. They can cause intermittent connections if they are not sized or installed properly.
I had crimped connectors on a used truck I bought w/ aftermarket speakers. After it had gotten wet (water in the doors from rain) a few times after several months one of the door speakers died. I found the crimped-on terminal had corroded and lost connection. I stripped the wire and soldered it to the speaker terminal.
You'll have to test the connectors to see if they are passing signal- on most of the very small diameter wiring (18-22 ga) GM uses, you should have pink Scotchloks. If you have blue or worse red ones, then they are too large. You may be able to isolate it to a certain wire(s) if you know which speaker(s) is/are cutting out. I know sometimes the wire's insulation can interfere with the connection after it is installed, especially if it is the wrong size.
I suspect the problem will spread to other connections over time if not corrected. The best way to tap into a wire IMO is to solder it. Otherwise you risk an intermittent connection problem down the road.
I doubt the sunroof was a factor in yours unless it had leaked by the particular connection.