I've got something of an oddly shaped small room (with many walls at different angles) that measures roughly 14.5' x 7' x 12' x 6' x 5' x 5' x 9' - not including the 8' high ceiling. Mathematically that works out to an area of 1,644,300 feet, which seems insanely big for one room in a house; however I'm quite certain that despite the math, the room checks out at less than 200² feet.
Anyhow I chose the M3 over the M4 because I preferred the 32 Hz spec to the 40 Hz spec. My previous speakers (boxes) were spec'd to 40 Hz and that just doesn't satisfy quite like bass down to 32 Hz. Personally, I don't see any point in using a boxed sub to go lower. OB bass is of a different quality (cleaner IMO) than boxed bass.
As for positioning / the way I have them arranged in the room... they are situated 4' off the front wall and spread 12' apart; the sweet spot in the middle is just a tad over eight feet back from each compression driver. I also have the speakers elevated so as to have the compression driver match the height of my ears in the sitting position. It took a few months of moving them around to get them into their final position, but all that effort was worth it.
Most of the listening I do is background / casual while I'm preoccupied doing other things off to the side. Of course all the magic happens in the sweet spot, but that's how it is with any speaker AFAIC, especially when it comes to sound staging and imaging.
There is / was member who used Odyssey amplification with his Spatial M series and he easily preferred it to the tube amps he had also tried, so I'm certain your amps will be fine.
If you decide to go down this route, remember they take a while to break in. I had to pound mine hard for almost 100 hours before they began to show signs of promise.