couple of questions for you guys 1. normally when people talk about changing the exhaust on this board, are they talking about changing the silencer (muffler) only or the change of the silencer and the cat back? 2. if I change the muffler and the catback, would it void my warranty? how about if I only change the muffler? 3. if I only change the muffler, does it mean that there is no gain in power (just a sound difference)???