What isolation feet under your amp with great result?

@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/

With nothing to do and all day to do it, I went and got out my remaining supply of Les Davis constrained layer damping pads and doubled up what I was already using, now with 2 under each footer on my Marantz PM15S2b integrated and 4 under the matching SA15S2b SACD player.

That was all it took to take it up the level of my Kinki EX-M1 in regard to extension, decay, clarity and almost, the impact. It's there, but in a different manner, and wonderful on it's own. It's like they are brothers who naturally speak in different tones but in similar manner.

I could live with either and am really loving the sound with the all Marantz set up. It's not as spot lighted as the Kinki but it's every bit as resolving, if that makes sense, and sounds a touch more organic. Before doubling up, the Marantz came close, but no cigar. Now with similar resolution, it's Arturo Fuente and Davidoff Signature all around.

All the best,
Nonoise

@rixthetrick 
What is on top of the amps now are two (on each amp) of these heavy little brass suckers that Dan finished in black with Isodamp elastomer material on the bottom:
https://edensoundaudio.com/shop/fatboy-disc/

I like the Isoacoustics carpet disc suggestion.  The smaller ones for the Gaia III are 1-11/16 inches in diameter so would fit a medium sized spring but they are 1.75 inches tall, which may be too tall for my situation.  I am thinking about how I could leave the Sound Anchor stands spiked to the floor and then put the springs beneath the speakers but that would negate the benefit of the additional 65-pound weight provided by the SA stands.  More consideration is needed.  First I will do some listening and decide whether I like springs under my amps before I modify my speaker set up.