Good to know you have things under control. I am allways suspect of any diagnosis by the dealer or any one for that mater. I hope they checked all the fuses there is a seprate one for the amps and there is also the Muting circuit for the cell phone. I still am not convinced that the head unit should be condemned.
Fuse 33 powers the head unit, fuse 51 powers the amps, does your antenna go up when you turn on the head unit. There is also a relay for the amps that could be bad.