Hi there,
I have a PCM2.1 dvd sat nav in my 997.1 too, and for what it is worth I have no desire to install a touch screen unit, as as this might be, I do want to keep the car as original as possible.
So to that end, there are a number of solutions in the market, which can add DAB, bluetooth for audio streaming and to connect any smart phone, whilst retaining the original Unit and use of the steering wheel buttons and use of the trip computer. On that note, if you have the Sport Chrono pack on your car, it might be preferable to keep the standard unit as well.... I am going down that route myself in the next month or so. A google search will give plenty of examples etc.
I live in Surrey and there is a supplier which seem to know their way round the various Porsche systems. I have no affiliation and I am not necessarily recommending them as I have not yet been to see them, I have merely been in contact with them and they seem to know their stuff. They also have loads of information on their website, including Youtube videos to show their work on 997s and other Porsche vehicle from this era. Worth a bit of your time just to get an idea of what there is out there. The firm is called Cartronics in Byfllet (around the corner from Porsche Brooklands in fact)...
Let us know how you get on... I will report back when I get mine done (I am going for the bluetooth and iPod connection only, mainly as I have a massive music library that will me busy!)
Hope that helps!