Karl, welcome. My first suggestion is that you not limit yourself to listening to 2-channel music source material on only front speakers. Using a mode such as DPLII, and especially with QS side surrounds, the enjoyment of 2-channel music is significantly increased. The natural ambience that's contained in the front channels(there was no place else to put it)although it came from directions other than the front is extracted and sent to the surrounds where it belongs. I never listen to 2-channel sources using only the front speakers when surround speakers are available.
The setup along the 18' wall should be fine. Separate the speakers far enough outside the cabinet so that they're about as far apart as your listening distance from them. As long as they're far enough forward to be slightly in front of the plane of the cabinet there shouldn't be any significant harmful effects caused by the cabinet.
I use and highly recommend for music listening(almost entirely classical in my case)the M22s. They're very flat, and in particular have no artificial mid-bass bump to add an inaccurate "fullness" in that area. For most music listening(excluding material such as pipe organ)they have sufficient bass without a sub, but this is something that you can determine after listening.
No special power requirements beyond the typical receivers rated anywhere in the 100 watt area would be present for listening to M22s at all safe(to your hearing)listening levels. I'd suggest that a Denon or Onkyo model with Audyssey MultEQ auto-calibration and room EQ be considered.
