Used RELs (ar any good sub) can be the way to go...I have a room about the size of the one described, and my single REL Q150E (circa 2001 10" forward firing) sounds great set around a third of its volume knob setting...adjusted slightly up or down here and there depending on the recording (I put a "chicken head" knob on the gain pot so I can easily tell what's what without turning the sub around). 2 RELs like this seem like overkill, but I'd buy another Q150E if I found a used one cheap enough just because I like it so much. Interesting article I read recently in a UK hifi mag about a REL sub...the writer was listening to some mandolin music and took the sub in and out of the system...you wouldn't think mandolins would have any low frequency information, but the music sounded much better with the sub on...go figure...I've done similar experiments and am amazed at how low the output on a sub can be and still add MOJO to whatever I'm listening to.