I took a quick look at the Axiom page for floorstanding speakers. Their recommendations were pretty clear :

- under 2400 ft3 bookshelf is OK
- over 2400 you want floorstanding; larger room -> bigger speaker
- M60 OK up to about 4000 ft3
- M80 recommended for >4000 ft3
- M80 plus 150-250w recommended for >6000 ft3

I think the room you're talking about falls into the >6000 ft3 category. Axiom's recommendations are obviously aimed at "filling the entire room with sound" and could be toned down a bit if you are OK with lower volumes or "filling part of the room", but at first glance that looks like an M80 room to me, M60s at absolute minimum.

Right now I am running M2s in the HT system and M60s in the main stereo system upstairs. The place I'm moving to in the spring has a 16x23 living room with high ceiling open to dining area and loft -- I figure the M60s will be the absolute minimum for that area whereas the M2s are just fine in the current area (one end of a low-ceilinged 13x23 room)... and the only reason I feel 100% comfortable with the M60s is that I don't really need to fill the entire space with sound, near-field listening will be fine.

M80 without sub really does sound like the right first step. Good luck, sounds like this is going to be fun !!

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8