Try the Megan exhaust. It's 600 bucks, deep NASCAR sound and is much quieter than the eisenmann but louder than the performance. It does have very very minor drone at 2k-3k but that's like 7th at 60mph. I love mine but want a louder one now.
///2013 AW 6MT E92 ZCP M3/// Black 359M Wheels/BMW Performance Carbon Fiber Spoiler and Mirror Caps/Arkym AeroSport Front Lip/Turner 15MM Spacers/LUX 8 LED Halo/IND Gloss Black Grills, Gills and M3 Emblem/30% 3M Tint/BMW Interior LED/MusicCar Subwoofer Enclosure/JL Audio 12" W6 Sub and XD600:1 Amp/Euro Sunglasses Tray/Ceramic Coated Megan Racing Exhaust/MS TP's/AFe Dry Air Filter/RPI Intake Scoops/Euro MDM/Feature Coded.