Looking at new exhausts for my 535i also. I have a friend with a Euro m635i that has a B&B TriFlo exhaust. It sounds deep and rumbly at idle plus at highway speeds it's pretty quiet and doesn't seem to resonate . It has a kind of throaty (and a little raspy) sound under hard acceleration that I'm not sure if I care for. Other than that, I really like the B&B although I have heard others say that it's much too loud for their tastes. My $0.02.