05 CTS radio install ???'S

I have A 05 cts. I am trying to put a Flip out DVD in. I want to install this without buying the harness, I jsut had A couple ?'s.

Where is the factory amp at?
Do I need to buy the harness?
I plan on putting a 4 channel RF amp in the car, with DD comps, so I didnt want to pay 200 for a harness I wont use, I do not need the onstar and will use the PAC controller. Has anyone did this or can they tell me how?

I jsut need to know which wires are which really, Power, Remote, Ground for headunit, and speakers for the amp, And is it possible to hook up speakers WITHOUT any amp at all?

Thanks!!
-Jon