[nick///M3]

from my experience with this car

best results honestly came from just changing the cats (100 ccpi HJS one's)
with the Xpipe from ss ( resonated or not depends on your prefer to noise..)

my set up

Stepped headers 63mm
Custom 63mm section 1 with magnaflow rasp terminator
ss Xpipe resonated
ss race Lightweight muffler
No drone no rasp and the oversize helped a lot for my engine's needs...