Darren a simple & proven solution is bubble wrap. Get the pink / red colored antistatic type (for longevity) place a sheet flat between the entire slab and your rack top. The sealed bubbles act as isolating springs & can hold the weight because you're using an entire sheet
Springs for homemade isolation stand
I want to suspend my granite top from my Sound Anchor rack w. some springs to create an isolation stand. I have about 100 -200 lbs of equipment on the granite top including a turntable. I was wondering if anyone can recommend a source for the springs that can support the weight & control resonance.