Having used SuperTrapp systems on various off-road motorcycles over the years, I just wanted to clarify a common misconception regarding SuperTrapp mufflers.
Adding additional diffuser discs to the stack will actually INCREASE noise and DECREASE backpressure. The first time I ordered a S/T, I wanted the motorcycle to be as quiet as possible since it was street-legal and I planned to ride it occasionally on the road... so I ordered an extra set of discs.
Imagine my surprise when my 12-disc SuperTrapp hardly deadened the exhaust noise whatsoever. I took out half the discs to reduce to the recommended number for my bike and then it simply purred.