No matter how non-resonant the cabinet might be, at least it's being bombarded from the outside by delayed sonic waves. Can you hear them? So can the cabinets. Apart from holding them in place, spiked stands allow the cabinet to transfer any resonant energy thru the stand down into the larger mass of the floor. With the cabs on foam, you've isolated them from the floor but broken the energy transfer. The spikes on mine are slightly rounded cones and yep they're blu-tacked too, right on the spikes! Blu-tack if nothing else is insurance against knocking the speakers on the floor, where a chip or dent might really change your whole mood.