I do not live close enough to be of any real help. But I though a few words is better than reading your thread and moving on...
The Hindle has a rather nice low rumble sound and is superior to the factory system.
The Two Brothers is a cross between a high end four stroke ATV sound and the Hindle. So it still has a very pleasing rumble type sound (Not the ratty cheap ATV sound), but not to quiet or two loud (Subjective I know).
Lastly... Every single Spyder owner that I have personally met (RS or RT) that have the Hindle always make a point in coming to me to comment on how much nicer the Two Brothers sounds compared to their Hindle...
And in no way shape or form would I buy a Hindle over the Two Brothers unless the law made it so or the price was almost free.

pps:
So there is my $.02