If I install an aftermarket amp (and speakers), I understand that I will lose things like navigation, bluetooth, etc. Is that true? Could I just install my aftermarket amp AFTER the factory amp? What are you guys doing to have an aftermarket amp without any loss of functionality?

FWIW, I have the non-ML system.

Peoples' amps go out and they say they can't hear the radio/audio. I've never heard of anyone complain that the door chime doesn't work.