It'll be fine. Mine are in a room 16 x 15 x 8 (drywall). It's carpeted and I use 4 Corner busters, 4 Echobusters, 2 pillows in each corner behind speakers and a big cloth couch. Powered by a MC402, it's amazing. I got by with just the Cornerbusters for 10 years and it sounded good.
The key is to be able to bring them out into the room. The backs are 3.5' from the wall and the outer sides 2.5' from the side walls.
From what I've read, the 501 monos are better than the 402. They'd give even greater control on the bass - which I can't imagine from how given how good the 402 sounds. I'd also recommend the HIFI Tuning fuses for the amp - a cheap beneficial tweak.
Relax, have a Lagunitas Kill Ugly Radio Ale and listen to some Hendrix...