I've had that exact X-pipe for about a month now. I had previously taken off the resonators. That X-pipe DID free up some hp, it is obvious during acceleration, and my mpg went up 2 mpg. It sounds really good with no resonators and that X-pipe. I personally think it gives the car a more Maganaflow type sound. Mine was also 2.5" and the muffler shop just used a couple of adapters. I had them install it where that big round muffler type thing is. Both pipes enter and exit this thing. Remove it and add the X-pipe. It is about 1/2 way down the exhaust, you can't miss it. I think it is used as a type of mixing box or crossover for the exhaust. It is not a cat because it has rolled edges and no sensor. A cat would not have rolled edges.