i got a custom cat-back made yesterday with flowmaster 2-chamber mufflers, and it did wonders to my 6.
http://s81.photobucket.com/albums/j230/mark97six/?action=view¤t=exhaust_0001.flv
http://s81.photobucket.com/albums/j230/mark97six/?action=view¤t=exhaust_0001.flv