I would stay away from granite. IMO, you need to ABSORB, not REFLECT. What I believe happens with granite for example, is the drivers move causing vibrations in the cabinet. Those vibrations travel down the cabinet, through the spikes, into the granite. Then, those vibrations bounce off of the granite, travel up through the spikes and back into the cabinet. I believe you should spike the speakers into a maple block to absorb vibrations. You can buy small spikes/cones and place them under the maple into the floor. Just my theory....
