Replace 2.5 exhaust with 'S' system???

[j.fro]

The mufflers are the same internally, so from a performance standpoint, there's no difference. The only difference is the appearance of the tail pipes. As for the catalytic converters, there are some major differences. The 2.5 is from cars '97-'99. These have two catalytic converters after the exhaust headers. The o2 sensors are fore and aft of these cats. For cars '00 and later, 4 cats are used, two for each side. The o2 sensors are on cats that are part of the exhaust headers. Because of this, the later cats could not be used on an earlier system without welding in bungs for the o2 sensors. I do not believe there is any hp gain from any part of the '00 and later system.
Emissions systems on all cars in the US are supposed to be guaranteed for 10 years...the Porsche dealer may (yeah, right) cover this.
If it were me, I'd try to have the cracked converter welded. If you are itching to spend some money, now would be a fine time to put aftermarket headers on the car.