You've got some great choices to finish off the HT in the QSx , VP150 and SVS.
The sound really will be excellent i'm sure of that.
I think somewhere not long ago we discussed how the speaker 'character' really seems to apply more for music than HT. I know i sure can't tell so much about the highs or midrange sounds while watching a movie but it's alot more evident when listening to music. If your primary task is for HT then both the M50 or M22 will do you well.
If you really are that worried about the possibility of knockover then don't think twice and go for the M50s for peace of mind. But, the M22s will sit solid on a stand that is properly weighted. Kids can push a tower off its spikes about as easily as they can yank speaker cables really hard....
Steve_C had a great suggestion in looking at the Axiom wall of fame page. You can get to see various Axiom speakers and their respective sizes in comparison to the surrounding furniture and such.
Links to my brief time with the M22 can be viewed here (clik on the couch panorama and you will see them next to the EP350, QS8s, a bar fridge, and futon couch):
my early HT pics with the m22s 
