I have had great success with the Coupling Disk made by Star Sound Technology. I use them on my hardwood floor, on my audio rack (so as not to pit the wood or metal) and on the bottom of some of my equipment.
http://www.audiopoints.com/
http://www.audiopoints.com/apcd2.html
You also might want to see if the company that makes the spikes that you use make a comparable product.
http://www.audiopoints.com/
http://www.audiopoints.com/apcd2.html
You also might want to see if the company that makes the spikes that you use make a comparable product.