What isolation feet under your amp with great result?

@mitch2
I have given the springs interface to my concrete slab some thought also.
Because of the need to as much as possible directly couple with the concrete slab with my stands, I have just purchased some solid copper spikes to go under my stands which sit on the carpet at the moment.

You seem to get my point of not having a yielding support under the isolation springs, and yeah carpet is going to absorb energy. If you have not got a spiked base solution for under your springs, do go directly to carpet, there is low surface area, another gentleman in Agon informed me that after he removed pucks from under the springs (he purchased Townshend Audio Seismic Podiums) even with the feet directly on the carpet it improved.

I looked for solutions, and perhaps you could look also?
I found these https://isoacoustics.com/wp-content/uploads/2019/06/Carpet-discs.jpg
Something like that under your speaker springs would be ideal, and that's why isoacoustics made them. You could DIY with a metal disc and three spikes much the same. But I must admit these look pretty, and aren't too ridiculously priced at all.

On top of your amps now that you have isolation in place, the next move is to DIY version of http://www.audiopolitan.com/blog/eti-amg-toppers-review/
I know .... yet another thing...

@sgreg1 - Actually I got a granite slab too, and put my springs on top of it!
https://systems.audiogon.com/systems/8721

My amplifier is 98lbs, and I have my DAC and server sitting on top of it, until I can build an isolation bench, low enough to not get up into the imaging area on the tweeter plane.

I would suggest spikes under the granite at least to try it out, I would myself, however I have already bolted together out of scraps at work, made of uni strut and double uni strut  frame upon which to test out isolation shelves for myself.

I've tried various things, but so far, the hard rubber feet it came with worked best with my heavy tube amp - go figure.  As many above pointed out, it really is trial and error.  

I like the suggestion above that good footers under the speakers might be a better place to start.  isoacoustics gaia's worked for me.  

@mitch2
http://milspecanchors.com/single-curve-spike-grid-timber-construction-made-in-usa/