don't worry about the volume difference, and all it should do is prevent standing waves inside the box, so it should sound cleaner. What's the worst that'll happen...you won't like it and you'll take it out?? Just listen to your system without it, then put it in...use staples or something temporary to hold it in place, and then listen to your system with it in there. If it sounds better with it (i think it will) then attach it permanently and enjoy! Unfortunately, I've never used that stuff, I use polyfill though and I like what it does.