I don't know, I had pictures rattling and shaking as if I had my PB13 Ultra turned on when I was in 2 channel and playing the M80s while connected to the A1400 and this was at ~80-85db. With the right amp I think the M80s could easily be used for HT with out a sub
For music I agree, for movies, a sub is a great addition. They really deliver a lot of bass but in WallE, I've made a few test and some sounds were totally inaudible when the sub was turned off. When you don't have one, you think there is nothing missing but when you compare some specific action scene it helps having deeper notes
