mattandbrook

The short answer is that none of the factory stuff works when you replace the head unit.  It all uses proprietary connectors.  I had to get a new camera, an adapter kit to interface between the steering wheel controls and the head unit, and a brand new Sirius receiver and antenna. 

I paid to have this done so I can't say for sure about 'how hard.'  The whole project took the shop about 4 days. 

The cables to the head unit are run under the trim on the drivers side and up the support pillar between the two windows.  No visible wires whatsoever.