I have a DC header, but it went on with the exhaust, so while I can't compare the Exmag to before, I can say that it's still astonishingly quiet, and sounds great. I'm looking to replace my cat with an RT high flow version, since it's still a cat and not a straight pipe, I shouldn't get an raspiness, but I'd imagine even if it were a straight pipe, the exmag seems to be so well resonated that it might muffle out the raspiness. I'm actually looking forward to what it'll sound like with a high flow cat, maybe this kitten will turn into a lion
Ask around, there are quite a few Exmag owners (most of whom had a good word to put in when I went shopping for a catback, and subsequently are the reason I purchased one) and I'm sure at least one of them runs a high flow cat.