E90/E92 m3 guys have been hacking open the oem exhaust and modding .

OEM Exhaust mod by Bimmersport Automotive - BMW M3 Forum (E90 E92)
REVIEW: Bypass OEM Exhaust Mod - BMW M3 Forum (E90 E92)
E92 M3 OEM Exhaust Mod..... - BMW 3-Series (E90 E92) Forum - E90Post.com

anyone willing to try or know how the inside piping of the stock exhaust is?

With the Akra system completely bypassing the muffler i'm sure we could get similar results by rewelding the oem exhaust.