It is my understanding that the Brembo big brake upgrade described in the following article is very similar to the "S" brakes:
Pelican Technical Article: Boxster Big Brake Kit Upgrade - 986 / 987
The steps in this topic will probably match what you need to do pretty closely.
The bigger rotors and calipers should fit in the 17" wheels.
Here is another thread that covers some of the other considerations:
http://986forum.com/forums/general-discussions/45751-installing-986-s-brakes-base-986-a.html
Steve