My X6 was tuned by Dinan, and the exhaust was replaced with something more aggressive sounding. It has a gurgling type growl that is impressive when starting the engine, and even more so through acceleration. They also replaced the exhaust tips with black ceramic, so it looks pretty cool too. I posted a low quality video from my camera phone a couple months back at the Dinan facility when it was in Stage one (Stock exhaust tips in video). If you can wait, it sould be available for purchase before the end of the year and you get a full warranty on all their superior quality work.