Further Isolation for Spike Cups

I recently acquired a pair of Paradigm Reference Studio 100 v.2 speakers, which are placed on suspended hardwood floors. The bass and midrange response as well as sound stage improved dramatically when I removed the round brass feet and placed 1" dia. aluminum receiving cups under the spikes. I'd like to try isolating the speakers even further by attaching adhesive felt furniture pads or "magic sliders" (I think a kind of hard nylon) under the cups. I.e.:

http://www.acehardware.com/product/index.jsp?productId=20040426

Any sense of whether felt or "magic sliders" (or even something like rubber) would work best?

Thanks,

Jeff