I just replaced the stock headunit and speakers on my 2012 GT and have learned a few things:
- I installed the Boss steering wheel to get rid of the plastic one that comes with the base model. When I installed the new Pioneer 2400BT with the PAC interface the controls on the steering wheel all worked. No dealer programming required.
- Since I didn't have the pre-installed Sirius antenna on the back hood I put the antenna under the carpet on the back deck. There is a brace that the antenna fits perfectly in to. Totally hidden and great reception.
- I then had the car tinted and lost reception on Sirius. It turns out the tint had a metallic layer that interferes with the signal. I had the tint lady remove the stuff from the rear window and replace it with a ceramic base tint. Works perfectly now.