On my LS2 GTO, I had a pair of Magnaflow mufflers welded in place of the stock ones and got pretty much the sound that I wanted. Those Corsa systems are $$ but other than changing sound, they won't do much for performance.* I was considering the Corsa exhaust for my car but couldn't justify the cost for such little benefit. Most of the GTO guys seemed to be getting the best deals from MarylandSpeed.
*I'm speaking from my GTO experience. The stock TBSS exhaust might be more restrictive so an aftermarket system might be of more benefit. (Probably not $800 worth though.)