I think this should be OK. On the subwoofer front, a couple of companies are selling vibration absorbing platforms -- one called a "SubDude" -- a few inches thick which fit between the subwoofer and the floor and pretty much isolate it.

I'm not saying you need to get one of these platforms, just that subwoofers seem to work fine without having to couple into whatever they are sitting on.

In my case, I was thinking of raising my M60s 12" just to get the tweeters up to ear level

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8