I have the Termi's on my XDiavel as well. They are very loud without the dB killers, but the Termi's just don't sound that great with the dB killers installed, though. Earplugs, and getting a quieter helmet may help, too. I did notice that as the Termi's build up a little "dirt" in them, the sound isn't quite as sharp. The problem is, is that they're so short that the exhaust exits right in line with your ears. I love the way the bike runs with the new mapping, too. The stock muffler is heavy, at about thirty pounds, so losing the extra weight helps an already lively bike feel even livelier. Hard to keep the front wheel down in first & second gear at anything close to full throttle!
A helmet with a close padding around the neck area helps...but, in my opinion, still doesn't dampen the sound enough. There's a certain rpm that results in a sound that resonates in the helmet...it even messes up my Sena speakers. I use ear plugs and a plush helmet.
OK, I just put the DB killers in my XDiavel Termi's for the first time. After riding around without them since last August, I now think the quieter sound is just fine. The DB killers are just a straight through piece of pipe with no baffles in them. It does reduce that sharp, blatty sound that the Termi's have, but they still boom pretty good.