Just go with straight pipes...
They sound amazing, they are loud!!
http://www.youtube.com/watch?v=M1VI-rTaUmU
This is a exhaust setup with the bypass pipes, have the guy who built that custom setup for you do this and change the tips to what you like.
http://www.youtube.com/watch?v=EEPv_l6GBfw
My favorite video with current setup.
This is me approaching from about 1.5 to 2 miles away.
You can hear the car at full throttle in the distance but i had to back off...i was hiting going way to fast for public roads.
There are a few other videos with the new set up in different situations.
http://www.youtube.com/watch?v=Pw9bRcdOj-Y
By the way right now the car has stock cats, aftermarket headers, muffler and a supercharger. There is another phase of mods that are more agressive than what i have now.
Have a great day,
gary