amp platform suggestions...

Yes, I am currently using 1/2" Lexan shelves. Best solution I have found yet. And don't confuse Lexan with Plexiglas. Two different materials.

In time I may try two pieces of Lexan with a piece of acoustic felt in between. Not sure if that will be an improvement, but I want to try it. I have lots of Lexan so it's just a matter of getting around to it.

Fiddler - for a long time people recommended - and as far as I know still use Vibrapods between two pieces of material like Lexan.

IF the object is to have an inert stand, the shelves can and maybe even should be made of layers of material which have different resonant signatures.
Granite, lead sheet, sorbothane, hockey pucks, golf balls, tennis balls, Maple blocks, Lexan and many more.

Materials and most importantly the MASS of materials can be chosen to have conflicting resonant frequencies with the result being that when put together, they are nearly inert.
I had a turntable many years ago....a Dual 1209. The platter was made of 2 pieces which individually rang like bells. Together, it was like thumping a piece of silly putty.