Hi, Lonely Raven. Playground sand in a wood box with wood platform sitting on the sand makes a great isolation platform. Herbie's grungebuster Dots are beneficial as a decoupling interface between each sand box and shelf. Baltic birch plywood is ideal for the wood platform. You'll still want to upgrade from the stock component feet, for superior isolation/decoupling; otherwise you're not really taking full advantage of the sand boxes. Isolation directly contacting the component chassis is always most essential. Four Tenderfoot isolation feet between each component chassis and wood platform should bring out the best potential of the components. Then again, with Tenderfoot isolation feet, you might find that your present rack is sufficient as is.
Herbie's Audio Lab