We were very happy to get one of the early 2.5" Welter Performance dual exhaust setups to test with our DDMWorks supercharged Slingshots and we are pretty happy with the results. While driving the exhaust is still able to be heard, but since it exits behind the Slingshot now, it makes cruising around much more enjoyable than with the standard or side exit exhausts we have driven. This setup seems to be a nice compromise of sound and power that I think a lot of people will be happy with.
DDMWorks Slingshot Rotrex Supercharger Kit