Some interesting responses here...
Tvad, as much as I appreciate the offer, I think I'm gonna pass. But I did read all the info on Symposium's website, very comprehensive. I had never really looked into them before. But the more I read and research, it sounds as if there would be a very negligible improvement, if any. Perhaps that money would be better spent in cabling and/or power conditioning for my source, I don't know. It's quite a stellar system, IMO, just trying to squeeze every last ounce out of it and make it the best it can be. It certainly couldn't hurt to try some of the cheaper alternatives though, such as the rubber/cork sandwiches that Clio09 mentions. And I read all the info on the Cat/Tiger Paws, very interesting. They would look way cool under my amps, but they sound like they could be a bit cumbersome to use, and they're a little pricy, IMO.
Still not sure what "ringing" glass means and/or it's effects on my system, if any. Ever seen that compressed rubber high density flooring used in commercial applications? I have samples of that at home. I think I'll try cutting some small squares of it and slip them between the feet on my amps and the glass and see if I can discern any effect.
Maybe this will give me some insight as to what direction, if any, to take...