Sub usefulness in constrained placement situation

Placement not a problem with room adjustments. If I were you, I'd get the Revel B15. Use fast interconnects, e.g., Signal Cable Silver Resolution, to ensure sub doesn't lag behind main speakers. Don't fret too much about it. Just avoid using fast speaker cables with slow subwoofer cables and you should be fine. I think I still have the name of a guy in California who had good prices on new Revel B15 subwoofers. I'll try to dig it out of my files if you wish.
Best wishes,
Jay

I used an HSU VTF-2 in the configuration you're describing, behind the couch, but with less space between it and the back wall than you're describing. It worked extremely well in my space. Give it a try. The sub fit perfectly underneath a very narrow, long table that was just the height of the back of the couch. I can't use that setup where I now live but I preferred it to my current configuration.

Thanks - I really appreciate the help and real world examples !! The end table idea is another option as well, though the WAF threshold will be higher there.....Thanks again.

I bought a DD-12 because of the need to control a difficult room, and because I only had a couple of locations to place the sub. My main speakers are Thiel 3.6's (as I said, major room difficulties, or else I would not need a sub) driven by Theta Digital Enterprise monoblocks. At first, I was skeptical as to how the DD-12 would fare in such company, but I have to say it showed its mettle in spades! Truly a fantastic product! Not only does it provide you with a great level of control over numerous variable, but it is just inherently a dang fine sub.

Accordingly, I would strongly recommend the DD series for your application.

Tom.