I just bought 4 more Axioms and a new Anthem MRX-1120 receiver to go 7.1.4.
Here is my take...
I had a room (v3.0 of my theater) that was about 11 x 15 x 8. I was using M60 fronts, VP150 center, and QS8 surrounds in a 5.1 setup. The M60s were MONSTERS for that room. Better oversized than undersized, but still I think that with a good sub the M22s will work nicely.
As for configuration, 5.1 was plenty in that "small" space, but if you wanted to do a step up from that, I would say a 7.1 using front wides would yield better sound than 7.1 using rear surrounds. If you wanted to go even more than that, I would go 5.1.2 or 5.1.4. The front overheads from the X.X.2 or X.X.4 setup will fill in the gap that the front wides would normally do, but give you that "height" element. If you went 5.1.4 then you would also be adding rear height too and probably be just fine without rear surrounds.
With all of that said, yes you need a good base set of speakers 5.1, 7.1 etc to really appreciate Atmos or DTS:X, but you will not get sound that is "enough" with adding more speakers to the traditional layout (7.1, 9.1, etc) to make it sound anything like Atmos. Also, the QS8s will actually work against you if you got an Atmos capable receiver. You want "pinpointed" sound, not a big spray of sound that the QS8s do (which was AWESOME for pre-Atmos configurations).
Yes, just getting an Atmos receiver and not having overhead or reflected Atmos speakers will be in improvement over a non-Atmos one, but you are just getting a taste of what Atmos can do and really need sound coming from overhead to have a truly amazing experience. YES ATMOS AND DTS:X ARE **THAT** GOOD... They are not gimmicks, and you will be amazed at the improved soundfield created by adding height speakers.
Heck, I just shipped back four QS8s that I replaced just over a year ago with on-wall M3s because I know that I HAD to have Atmos and Atmos works best with monopole speakers (not di/bi or quad pole like the QS8s). Heck, Atmos and DTS:X are SO good, that I am basically dropping $3500 just to add it to my room. $1000 in speaker, and $2500 in a receiver (replacing my previously "most expensive to me" receiver that cost me $800 4 years ago)...
Hopefully this helps in some way or another.
The nice thing about your room size is that even if you go "all out" for something that size with a 5.1.4 (or X.2.X if you want to count both subs) is that there are a number of 9 channel receivers out there so the price is a lot better. For my 7.2.4 setup, I had about 2-3 choices if I didn't want to add an external amp and it is costing me...
