You ought to just get a replacement muffler. The stock exhaust pipe is stainless steel and is mandrel bent, so the aftermarket "cat back" systems are really just a waste of money. If you want different tips you'd be better off just buying them and saving the other money. If you don't like the flowmaster you can just find another muffler you like and have it welded in.
I bought a cheap SS muffler on ebay for something like $40 and some mandrel bent aluminized pipe and welded it all up me and a buddy and replaced the downpipes after the cats, the y pipe, and the muffler. This is more performance than you'll get with that cat back and I think I only spend like $100.
Breathing in and out is good enough for me.