A friend of mine made his own custom exhaust with an X-pipe and Spintech's side exiting mufflers on his LS1 powered Holden Torana and it sounded pretty BA and looks neat.
[ame="http://www.youtube.com/watch?v=oIrkGq_2aBc"]Holden Torana LX with LS1 and Spintech mufflers - YouTube[/ame]