My room is almost the same dimensions with a vaulted ceiling and sized attached dining room and kitchen as yours and Iíve tried the M80s, M22s, and M2 and feel the M80s are the clear choice for both music and movies. On big thing to consider is how far you plan to sit from the front speakers, the farther (8-10 feet or more) the more you will want M80s.
Another thing to consider is whether you will be listening to music while in the other area attached to your theater. This is because listening to 2 channel music (not much need for surround if say youíre in the kitchen) may sound better with the M80s because you wonít need to use a sub to get good bass. This is important because placing your sub for the best theater experience may likely give you boomy bass in other areas like an attached room. Itís less likely this will happen with the M80s.
Yet another thing to consider is sub calibration/placement. Sub placement is tricky because of trying to get even bass throughout the listening area which is made more difficult the larger the range of frequencies the sub must cover. The M80s go down to 40Hz with authority meaning the sub may only need to cover below 40Hz. The M22s only go down to about 70-60Hz with any authority meaning the sub must these higher frequencies making it more likely you will get either boomby and/or anemic in some of your seats.
Something else to consider is how loud you plan to listen. The louder you want it especially if you seats are farther from you speakers the better the M80 will handle the midrange frequencies without any problems.
As you can see Iím leaning you toward the M80s based on my experience in a similar room.
OTOH I think that the EP500 is more than a match for that size room. I had to rearrange and fix some things in the kitchen because the EP500 shook and rattled things in there so much. The reality is that there isnít a whole lot of bass even in movies down below 20Hz (waterfall graphs on AVS aside). I know this because I have a bass shaker (Buttkicker) and with every movie Iíve ever watched (plenty of action movies) I have to set itís filter to play up to 40-50Hz, usually 50Hz to get much out of it so IMO the extra bass extension of the EP800 just isnít worth the premium. However, taking the money you save and getting a bass shaker for your seating (they run around $400-500 for a full setup) it IMO worth it since not only can it directly shake your seating (meaning the sub doesnít have to) it can do it even when the movie only has higher bass up in the 40-50Hz range but by shaking your seating it simulates earth shaking low bass even when it isnít there (and should be).
Iíve got to run but those are my quick thoughts.
3M80 2M22 6QS8 2M2 1EP500 Sony BDP-S590 Panny-7000 Onkyo-3007 Carada-134 Xbox Buttkicker AS-EQ1