'03 exhaust question - recommendations

Hi - I have a 91 5.0 that I know all the in's and out's and have done just about everything to, but my wife now has a '03 and I need some recommendations. I want the car to sound throaty, on the older car, I have flowmasters, but I'm not sure if that's still a good muffler for the 4.6L. I really want the deepest sound. Also, does a muffler change affect the factory warranty? Thanks.