I have a 2006 and wanted to do the same thing. I went to Tweeter to talk to the install guy and he said he has installed some systems in 997's with the Bose system. I saw some pics and it looked great. So, I am thinking of getting a Pioneer AVIC installed. I have the Bose system. I also found this on Caymanclub.net.
http://www.caymanclub.net/cayman-electronics/22732-avic-d3-installed-bose.html