My 02 Z06, which sees exclusive track use in a stock based class (SCCA T1) still has stock headers and cats but a straight through pipe after the cats. The sound is nothing like stock.
There are lots of aftermarket exhausts from the cat back that really can change the sound of the car. I don't know enough about the specific's of each brand to help you, but I can tell you that it can be done without touching the stock headers and cats.
