Your car has two sets of cats. One set is integrated with the manifolds and the other is downstream by the muffler which are probably the ones you saw. The bypass pipes delete the 2nd set of cats by the muffler. Here is a pic of the stock system off the car next to fabspeeds pricey system. Use of the cat delete pipes yield about 5-8hp gain typically and a little more sound.
You don't want to elminate the warmup cats or you'll get those CEL issues. Maxpeed makes a more economical set of headers with cats if you don't feel like dropping $2,300 for just the headers alone. They also offer cat bypass pipes and mufflers. If you talk to them about the whole set I believe they offer you a price break.
http://www.maxspeed-motorsports.com/986exhaustparts.html
Threaded Mode
