as i am in a dorm room right now i would say that the m3ti would not be to big. and i have a ton of crap in my room right now.
if its university dorm, where the rooms are smaller, and neighbors can here everything you do, i would go with m3ti's, not m22tis(also its more expensive)
but-think down the road. Next year i am moving into my frat, and ill have more space and ability to play loud music. if your son will also be moving out of the dorms, he will be able to support larger speakers better. I recomend speaker brakcts(the m22tis can be wall mounted)-which basically takes up a minimal amount of space when on the wall
