I don't have any experience beyond the Nordost Sort Kones that I recently purchased and put under my CD player, but I can pass along a story the owner of the audio store told me. You can take it or leave it.
He was helping a friend optimize a system that was getting some vibration related feedback though the turntable. They discussed several isolation ideas to keep the vibrations from the speakers from getting into the turntable. In the end, they used a set of Sort Kones and it was "cured." They were surprised that they worked in that situation, but very happy with the results. They use them under just about everything in the store.
He was helping a friend optimize a system that was getting some vibration related feedback though the turntable. They discussed several isolation ideas to keep the vibrations from the speakers from getting into the turntable. In the end, they used a set of Sort Kones and it was "cured." They were surprised that they worked in that situation, but very happy with the results. They use them under just about everything in the store.