@drrsutliff thanks for your input. Currently I guess my observation is that adding vibration control, at least the type I used, was hugely detrimental to the sound of my amp. Which seems to possibly imply that the sturdiness and solidity of the foundation it sits on matters more.
I do have a heavy wood shelf that all of my gear sits on, but given the Diablo’s apparent sensitivity to the foundation it sits on, I’m wondering whether it’s possible to optimize this even more.
After removing the vibration control the sound has become much more solid, fuller and with more drive, energy, and far more bass response, with better soundstage depth and a more coherent and natural easeful presentation. Truly transformative.
Update: currently I have 4 of Herbie's "Giant Fat Dots" between my wooden shelf my gear sits on and my wood floor. I am now wondering based on my experience if instead of vibration control padding under my shelf, my amp would prefer it if I installed coupling spikes under my rack. That said, I did notice a net gain in sound quality when I installed the 4 pads under my shelf. But that may be due to the benefit to my other components. Definitely warrants further experimentation I think, and this time I'll be more careful to gauge the impact of EVERY tweak.