What isolation feet under your amp with great result?

Another vote for AV Room Service EVPs.

If it ain’t broke, don’t fix it.
After reading this thread I tried some footers under the amp.  Deteriorated the sound.  Removed them.
Happy camper! 

Please check out this source of vibration isolation study and application:
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=8275

I have purchased a number of electron microscope isolation tables for use in taller buildings that have vibration/oscillation/sway properties taken into account.  Very interesting reading.

Iso Acoustics IsoPucks. Inexpensive and very effective. Your amp might be at the upper extreme of their mass limit though.

Pure isolation dont solve the resonance problem...

Solving the resonance problem dont solve the isolation one...

Some trade-off is necessary....

I chose a low cost homemade coupling/decoupling way with diverse complementeray materials... It works well for me at peanuts cost ....