Most racks these days are claimed by their makers to provide isolation to the components placed in them. But do they? The spiked feet often found on their legs, and the spikes or cones intended to isolate the shelves from the rack's structure, are actually couplers, not isolators. Vibration is free to travel up into the rack from the floor it sits upon, and into the shelves upon which components rest. Not good.
Townshend Audio has a true isolation product named the Seismic Pod, a spring-inside-a-"bellows" design. The Pod is available in sets of four, attached to outrigger bars for speakers, and also bolted onto dual-Pod 90 degree assemblies for placement under the four corners of a rack. If you use the Pods with any already owned rack, the nature of that rack is of insignificant consequence. Townshend also makes it's own rack with the Pods built in. For details look on the Townshend Audio website.
If the Seismic Pod products are out-of-budget (they're not cheap), there is always the modestly priced roller bearing, which isolates in all planes but the vertical. Add a vertical isolator (a spring, either mechanical or air), and you have excellent isolation at a fraction of the price charged for nice looking, but non-isolating, racks. By the way, the currently-in-vogue maple shelves may sound "pleasing", but they provide no more isolation than does any other wood, just a more pleasing coloration.
