I strongly recommend the Avic D3
Recent Install - DVD Navigation
The instructions from Trillionare are awesome and I've gotten sooo many compliments on my new setup. I did it all myself $699 for Avic at Best Buy and a few bucks for the install kit (follow the threads on the link and you'll find itr on eBay). I also upgraded the amp and it rocks. I was just jamming to the new Rush album Snakes and Arrows and it rocks!
Good luck. Remember it's a Porsche so it deserves the best!
-Steve