We can sell you Fabspeed, Akrapovic, Eisenmann etc. For the $$$, we really like Fabspeed. It sounds absolutely awesome, esp with XPipe. Stop by to hear our VF620 car with full Fabspeed system
Akrapovic is without doubt the finest system made for the M9X M but you are paying a lot of $$$ for it.
Both are great, it really comes down to budget IMO.