Nickway, FWIW, I have achieved the best results in DIY isolation products for components and turntables, much the same way as you have, by using a sandwich of materiels, usually a soft wood and a medium density foam product. What I use depends on the sensitivity and the weight of the component, but my purpose with all components is to prevent incoming vibrations and to allow the vibrations from components (either airborne or self generating (as in CD players) to flow to a substance that is absorbent such as soft wood. Unlike others I don't subscribe to hardwoods or stone products, and I usually want the mass of the vibrating component to exceed the mass of the substrate. IMHO sandboxes can work just fine with the sand taking the place of the foam product. FWIW, except with ultra sensitive equipment, I don't believe in fussing too much about this process. Much of the damaging vibrations your system will experience are airborne and most the damage is done before the vibrations reach the control devise. The cost of materiels is relatively cheap and its a fun Saturday project in the workshop. :-)