I have pretty much the same system you are describing and would recommend 5.1.2 if you can swing it but if you need to invest in the sub first, forgo the ATMOS in favour of the bigger EP500 Sub.
I recently upgraded from the VP150 to the VP180 on wall and there is a huge improvement, almost overkill. Kind of wonder what the VP160 would have been like but I have no regrets.
Upgrading from a ported EP175 to a sealed EP500, on the other hand, was a HUGE improvement. I'm not exaggerating here. You always wonder if the extra money is worth it and this is one of the few upgrades I've made that leaves absolutely no doubt. The proof came in the form of my wife racing down the stairs wondering "what the hell was that?". I'm now wondering if I have room for the EP800 or get a second EP500...
Now, M2 vs M3... I'm going to go against the others and recommend the M2's as they are a better match to the M22's with both having 5.25" woofers. I know the VP160 and VP180 have both the 5.25" and 6.5" woofers but surrounds will likely be set at 80hz and if you get a big enough sub, it will take care of any low end.
If, on the other hand, you get something other than the M22's (M5HP or M60), then I'd go with the M3's for surrounds.
