I am in this business for over 15 years of time. In the past I sold a lot Rel subwoofers. Beside this I have done many different tests with subwoofers as well. I would only choose for downfiring for surround. When you have an ols house or woodenfloor you get more drive. The floor makes the low freq even more pronounced. Even with music it can give some more fun. But..... when you want the best what i call steatlth integration with your speakers a closed subwoofer with only one bass unit in front is the way to go. Also in timing and speed this works a lot better. When you have a very fast subwoofer in respons you can use to higher freq. I use mine from 16 hz till 140 hz. From 80 hz low freq. become touchable. With audyssey pro and using it till 14o hz I have full stealth integration with my subwoofer. In the past I thought that this level never would be possible. Time and technique changes and sometimes dreams can come true.
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.