I am reminded of the other part of the can of worms when coupling to the floor - what the floor itself sounds like. A cello, washtub bass, etc. actually play the floor, but we don't want the speaker to play the floor. I like the idea of isolation feet or platforms that decouple from the floor, while still providing rigid non-recoil. A conundrum. What products out there come close to filling that bill? No springs or sponge. Yes to decoupled rigidity. Any thoughts?