Do I need isolation footers for my components if I'm already using an isolation rack?

My sandwiches of different density materials works fine for me ….Quartz feet, granite plates,cork plate, bamboo plate, sorbothane sheets, all that in sandwiches seems to controls the resonance and vibrations of my gear that is on my desk...

One day I will try, springs, and crystals beds under the speakers also...

I use whatever LIGO uses. I.e., mass-on-spring. It’s not rocket science, folks. 🚀 Well, maybe it is!

I don’t think it’s possible to have enough vibration control, but it’s all system specific and experimentation is necessary. There are no magic bullets. In my own system, I use a combination of granite and Rock maple sheets, roller blocks,SR 1.0’s, vibrapucks, and Bindbreakers (made in Lithuania, from steel and bog wood). What you put on top of a component is just as what you put under it.

Yes.

Ingress Engineering are very effective. Combine with a slate or granite platform and a spring they are even more effective.