Solo Mach XL J pipe system is reasonable at light throttle under 2k rpm with headers, catless. It barks loud WOT though. I love it as there is zero drone now. I had a 3" MBPR system x piped and swapped out the x for the resonated H and the drone still killed me 1400-1700 rpm.
As was posted above, it's gonna be loud under load no matter what. My wife commented on how much quieter it is now, she doesn't hear me leave or come home like she used too. The j pipes really work at low RPM.
Another 1 of 371 '12 T3 LS3 M6's built.