Hi fellas,
Fitted up an Xforce centre muffler and Y Pipe Assembly on my H6 lib and slapped a genuine pair of TB STi Quads on it and it is the most delicious blend of sound quality, noise, and lack of DRONE! Zero drone at any rpm, quiet and respectable when driving relaxed, grunty (but not LOUD) when being generous to the throttle, and just mint (and very audible) when WOT, if you fang it, everyone will hear you. A true perfect exhaust system.
Just thought I've give some of my experience in the matter for those looking for an exhaust system for their h6. As much as I'd like to have a unique exhaust set up with the TB STi Quads, I couldn't help but share this secret with you fellas