On-walls are a great choice.
The M3 are too warm-sounding. The M5 are too much for your room but with AccuEQ on your Onk, you can tame them nicely.
M2 would work really well. They are more accurate than the M5 within their range. In your smallish room, the bass from the M2 would get you by until you get a sub.
The M2 will also be an easier load on your Onk. The M5s, with their large motor on the woofer, demand some power. Note your Onk is not continuously rated for the 4 Ohm load the M5 presents. The M5 will function but it may not perform during dynamic pieces.
I have M2 and M5 on-walls as music fronts for my 1900 cu ft living room. I use the M2 exclusively now for music.
