There is an easy (but expensive) iPod solution - the Dension Gateway 500. AFAIK there isn't a Bluetooth option for it yet.
The problem with the CDR23 and Bose system is that they use the MOST fibre optic connections between head unit, amplifier, CD changer, instrument cluster and phone, etc., making it difficult to integrate normal wired technology. If you want to replace the head unit, then you are looking at a new amplifier and speakers too.
Dension have just released their Gateway Five, and I believe they may be working on a solution for Porsche MOST systems. http://www.dension.com/en/multimedia-adapter/gateway-five . It might be worth dropping them an email to see if they are, and a release date.