For what it's worth, I just ordered a Supersprint street muffler system for my 09 X6 3.5. The system is made in Italy and takes 7-10 days to get to the US and then another 3-4 days after that to get to the customer. The sport model, although I didn't want it, was not in stock and could take some time to get one. Not a cheap system, about $2500 plus install but I surely don't want my car too loud. Supersprint claims a two decibel increase in sound and seven HP, two ft/lb boost.