The discussions on this thread got me thinking about those cork blocks and the fact that I have a few left in the basement. So yesterday just for kicks I tried putting them under my subs. I have 2 Carver True Subwoofer Super Juniors. I had then up on spikes,but to prevent the spikes from damaging the wood floor in the living room I finished a couple of 12x12 pieces of 3/4 inch I had laying around to match the floor and put them under the subs. So just for what the heck I put 4 of the cork blocks between the wood squares and the floor.i didn't expect much, but boy was I wrong. the subs tightened up and sounded better than they ever have. I guess the wood squares sitting directly on the floor were transferring too much energy to the floor itself cause the bass to sound loose. It seems counter-intuitive that the combination of coupling the subs to the wood squares but the isolating the square from the floor would provide such good results. You never know what will work until you try.
Next experiment when I get the time and energy will be to pull out the spikes and see how it sounds with the subs sitting directly on the decoupled wood. It may be better, it may be worse. The only way to know for sure it to try it.