I used a Sub Dude with my REL B3 but didn't note any improvement versus the sub on the carpet. The floor is concrete. Of course, I never could achieve the result I wanted with the B3 either. I now have a pair of Gallo subs which actually do what I want. They sound and look great on black marble tiles.
What's under your sub?
Some sub manufacturers recommend placing a down-firing sub on a slab of marble/granite when the listening room is carpeted. Has anyone had any luck with that? I tried using a granite slab under my REL Storm III and found that the bass was much cleaner with the sub on the carpet and not on the granite. I have carpet over a concrete slab. Don't know if that made a difference.