I replaced mine. I had the CDR23, amplifier, CD changer, dash speakers and door subwoofers so not the Bose option. I replaced the headunit with a Pioneer 940bt satnav unit and a Alpine amplifier as you cannot keep the Porsche amp as it's fibreoptic only. I found a replacement that fitted in the frunk on the bracket where the OEM amp used to be.
First thing I did was add rear speakers, shortly after the headunit and amplifier, last thing were the dash speakers. The only wiring I replaced was for the dash speakers and I used the head unit to power the front and rear speakers off the head unit and the door subwoofers from the Alpine head unit which works really well. The problem you have is the subwoofers in the rear shelf, these are 1 ohm but there are others can help you with this.
Here's mine. As I said, I dont have Bose but can help with anything else:
