The MOST system in late-model Porsches is touchy when it comes to aftermarket installs, so make sure whoever installs it has experience with them, or you'll end up paying a dealer an hour's labor to get it working.
Most Porsche people prefer to stay OEM. Definitely hang onto the OEM head unit, ie don't sell it, because the car will be harder to sell without it.
'09 was the first year Porsche offered Bluetooth, but even to this day it's only for phone, not streaming. See if yours has the Universal Audio Interface. It's got 3.5mm, 30-pin iPhone, and USB ports. I'm not sure where it's located in a Cayman, in the Carrera it's inside the center console cubby. USB is only for charging; 30-pin you'll need an adapter to lightning-plug for the newer iphones, and it will NOT charge the phone. You could use a 3.5mm to interface, and the USB-lightning to charge, but then you won't get on-screen control. Basically it's a stupid, outdated system.
There is another way, which is what I use on mine. It's called an iSimple Tranzit BLU HF. Costs about $100 on fleabay, plus another $25 for a Motorola-to-PCM antenna adapter. Gives me hands-free phone plus streaming for music and GPS.