I was at White Bros this afternoon picking up another E-series. Since it's white bros pipe and an unusual shape, they're (or one of their distibutors) the only source for inserts, I think. It may be that distributors don't carry it, but I've seen them in the wb catalog. I've three buddies running the megaphone version of that pipe and they all love it. We didn't think it was that loud, stock with 12 discs and we're sensitive to sound pollution. You could try removing some discs first, which may compromise some top end and benefit bottom end. My guess is that anything that further restricts that exhaust will cause some negative power effect, but I don't know about the quiet insert. I'd call white bros. They did a lot of dyno testing with their e-pipe and they may have dyno data with the insert installed.