Although the M60s are theoretically occupy about the same floor space as M22s on towers, in actuality they seem a lot bigger. If you seriously consider this route, block out the space or better yet bend an old cardboard box into the dimensions of an M60 to ensure you've got the space.
M22s+sub vs M60s with no sub is a very close call. You could keep the M22s, attach the stands, put lead shot in the stands, and get a Hsu STF-1 ($300). That's a great sounding setup and would probably be OK safety-wise. OTOH two M60s are about the same cost as M22s+stand+STF-1.
I've had M22s + STF-2 and M60s without a sub. Both are excellent. I very slightly prefer the M22+sub approach, simply because I like plenty of bass. But the M60s have adequate bass by themselves, and (to my ear) a somewhat better upper bass/lower midrange.
I guess how much home theater vs music is the final decision point. If more HT, sub is probably better. If more music, the M60s are probably better.
You can't go wrong either way. Both sound great.
