I believe RC has tried the Monster Cable iPlay and liked it
(web page). It's still an FM transmitter but maybe one of the better ones. You can also use an FM modulator that is direct wired to the antenna input of the Cayenne sound system. I have heard that Kenwood makes a good one
(web page). There is not a way, at present, to directly connect into the modern Porsche sound system. It is a proprietary, fiber optic system with no auxillary inputs. Dension USA continues to promise that they will have a Porsche MOST compatible product soon but they have already missed a couple of product deadlines so don't hold your breath
(web page).