Decoupling Speakers

You make a good point @millercarbon 
Just this morning I ordered springs for under my speakers so I could compare with the Herbie’s gliders.  I will not say “never” on the EVPs but $800 is a lot of money.
My hang up with springs under my speakers has been stability but I was able to find some that fit my desire for a relatively low profile, while being at least 1-1/2 inches wide for stability and working well within the compression range needed. I ordered one extra spring per speaker in case I need to even out a heavier weight at the front or rear.  I also have some rubber furniture leg cups coming that I can place on top of the springs to reduce the risk of slippage between the spring and the speaker.  I am considering bolting those to the bottom of my speaker stands (through the existing threaded spike holes) so they are stationary and then I can slip the springs up inside of them......maybe not needed but it should make me feel like they are more secure compared to having loose springs sitting beneath my heavy speakers.
The springs I recently put under my amps (in place of Stillpoints) have been an impressive solution so I look forward to comparing these with the Herbie’s gliders under my speakers.  It would be really cool if the springs work out as a low cost solution under my speakers since I also have two heavy subs I could then decouple. 

You could do all that. You could also use carpet tape. The front will be heavier than the back. Tape the four in the corners for stability, leave a 5th free to move for leveling.

Interesting. Your floor structure sounds very similar to mine. Very solid and good for not contributing sound itself which I find to be very desirable for clean , articulate detailed sound where floor interactions in the bass region in particular do not obscure the detail in the midrange. Interested to hear what the decoupling sounds like compared to prior.

the only reason to decouple is if something is being excited by vibration and it becomes audible.  
your floor is being excited but it is massive and solid enough not to be audible. 
your stands are also high mass and rigid and doubtful they are being excited enough to be audible.  
this leaves your speaker enclosures.  
they are most likely excited on occasion to the point of being audible.  since they are bolted to your stands the energy from the enclosure is being reflected back to itself and this is also likely to be audible.  
you can decouble the system at the floor, but as long as you keep the speakers bolted to the stands the stands will reflect energy back to the speakers.  
your best sounding option is to decouple between speaker and stand.  

@avanti1960 

your best sounding option is to decouple between speaker and stand

That is a consideration, but the trade-offs are the loss of the additional mass provided by the stand and the additional stability resulting from the outrigger effect of the stand being wider than the relatively slim speaker.  I will consider that but I am not really comfortable from the standpoint of stability.

The good thing is that it all sounds good now so the changes will either sound better and stay or I will go back to the current set up.