I ended up buying an SVS, but during my research phase, Sasha at HSU recommended that to diminish the risk of pissing off neighbors, you can place the sub closer to the listening position, like beside the couch. That way, you can often play the sub at a lower volume, and the sub could be further away from common walls, with no real negative effect on the sound of the sub. Might be worth a try.
If the M22's are sounding thin, you can try turning up the tone control for bass on your receiver, or experiment with how close the M22's are from the wall. I have the bass knob on my receiver turned up past the center to give the M22's a bit fuller sound, but my sub definitely provides the low end punch.
Good luck, hope you can work it out.
