There are a lot of good stock rear diffs, it would just take too much money/effort to make them work... I'd take a Toyota TRD from an old Supra if I could... my buddy puts 700hp through one running mid 9's...

BTW, after much research, the AMG/SRT-6 rear uses ALL the same components as the N/A 6-cyl except the ring and pinion (gear ratio)... hence why the tiny spider gears didn't stand a chance...