I have not heard the M2 but own the 4367…. So peanut gallery comments below.
Since these speakers use the same drivers I think the biggest difference will be the dispersion pattern. The 4367 is a good bit narrower than the M2 due to horn pattern. The M2 will have more room interaction (soundstage) which could be good if your room supports good side wall reflection (symmetrical, enough distance to the walls). The M2 is also far more adjustable to taste.
If you don’t want subs the M2 will have deeper bass. I like the placement flexibility and shear power subs bring…. I realize many don’t want subs and the M2 would probably work better in that use case.
personally the tonal balance of the 4367 which is a bit warm/rolled off but detailed and dynamic at the same time is just right for me. Any music style (good or poor recordings) at any volume level is fine. Looking at the measurements of both I would most likely add a -2db filter from 8k up on the M2. I personally hate fiddling with my audio and chose the 4367 for that reason. I do technical work and just want a “simple” system for music but I would guess better performance can be squeezed out of the M2 if you are will to do it.
there is a very good deal for a new in the box pair right now.
Measurements of both at Erin’s Audio Corner.