07 Suburban audio/rear a/c issue

[cm000]

Just acquired an 07 Suburban. It had an aftermarket radio/cd/dvd player installed. It was put in because the previous owner de-installed the previous aftermarket system. As a result, the rear a/c and rear radio do not work (appears no power to rear unit - though the rear heated seats work) and the audio volume controls on the steering wheel do not work.

The local chevy dealer looked at it and said that the radio was not communicating to the amp (although the the audio was playing fine in all systems/dvd and indicated that the rear air needed to communicate with the amp/radio in order to work. The dealer recommends reinstalling teh OEM radio.

Before we do that, we wanted to know if there was another solution. I've seen mention of 'interfaces'; is that the solution?

Thanks for any help

[CanadianBacon94]

My rear air barely works with stock radio