If it is Just sound you want with no drone. Do the oem exhaust mod perf pipe replacement. It will run you $300 at your local muffler shop and the sound is on par with the MPE only a tinge louder from what I understand.
Your foot is the volume knob, and there is no drone (above stock) to note. You will not believe that you have an exhaust that sounds the same or better than a $2-4k aftermarket muffler.
09 Space Gray E90 M3 DCT: BPM (Stage 1, DCT and Servotronic) tune, Gintani Sport Exhaust, Dinan Intake