Hi Brian. Like you I am used to a high hp car that quietly whooshes on by with just the right amount of rumble... So I dumped the mufflers on my GTS and replaced them with a larger set of SuperFlow mufflers. The sound reduction has been much enjoyed, not only by me but by everyone that I pass under full acceleration.
Don't get me wrong, you still won't "sneek" up on anyone with this thing, but it sure is a lot better.
I also got a set of tips that point the exhaust to the ground but I haven't installed them yet. I'll let you know what they add when they're installed.