What isolation feet under your amp with great result?

For fun, I just ordered some springs yesterday.  I tried to go with something shallow enough so my amps wouldn't look weird and something wide enough for stability.  Regarding the spring constant, I ordered springs where the total weight per spring would be just a touch over one-half the spring's maximum capacity. 

I used some empty cat food cans under an amp the other day to raise it up and it sounded quite good. Can't really say if it helped or not.

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.