I think thats the nature of the beast... Im not sure much will change the sound as far as any other performance mods. The way it sounds is the way it is going to be... it might break in a little bit over time but it might get louder. I dont have the JBA evol so i cant comment on that but I have had both magnaflow and flowmaster mufflers on my previous vehicle and after a break in period it seemed a little louder. As far as using dynamat or any other sound preventing product it would be trial and error trying to dial it in to try and sound proof the cab. Id say your only real fix is if you dont like the way it sounds is change the muffler.