i recently got under my m6 at my friendly muffler shop and deleted the cats without the o2 sensors. you HAVE to leave those cats with the sensors alone. You can also safely eliminate the resinator and just have your guy put in generic "test" pipes. It only cost like a couple hundred bucks and everybody wants to know who's brand exhaust i use because it sounds pretty nasty up around 6-8 k on the tac. I kept the original mufflers on and i hade somebody drive my car so u can hear it from the street. I ve checked alot of websites with their product on an m6. my car now sounds better than some $5000 complete exhaust.