I didn't even know this existed. I was looking at building something similar as a custom a few months ago using a y-pipe and a Vibrant muffler and resonator with 3.5" piping.
'08 E90 335i 6MT. Under construction for a 'few good mods'
'09 E93 M3 6MT, H&R sports, Spec TwinDisc P-trim, UCP, FOR SALE
'09 Z4 sDrive35i DCT, MHD Backend flash, JB4, DCI