Can't really answer as to if you can use the factory SatRad antenna or not. As for using the factory amp, that should be part of the wiring harness that you would need to get in order to make it work with the existing wiring.
My '07 had the base system in it because I ordered it that way since I know I would be adding all my own stuff in. I replaced all the door speakers, put in two Alpine amps, and a single 10" sub behind the seat, custom built by JDBoxes (site member, but not making boxes anymore). For the satellite radio, I have a Pioneer tuner and the XM antenna is run out the third brake light and ont he roof. I had it on the dash under the center tray on the dash, but got a lot of drops there. That is where the GPS antenna is at though and it works well. Also I bought the adapterto make the steering wheel controls work the AVIC as well.
Great site for AVIC information is listed below.
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