Trust me, they all sound like chit on a V6. Try to find a muffler that hides as much of the high rpm whine a V6 has. Good luck bro...
Most all mufflers sound great at idle on a V6, it's when you start revving em up the sound goes to hell.
I know nearly nothing about this (as far as the sixers go), but I've heard Magnaflows don't sound bad- not sure if it's true