In reply to:
Speakers sitting on spikes or rubber feet help keep them in place, and disasociate them from the ground, thus reducing vibrations. Try them on the bare floor, then on the feet. You'll hear a difference, espeically at a louder volume.
Well, that depends on the floor structure and surface materials. If it is bare-wood flooring that is on top of joists and thus flexible, the "insulating" feet (such as rubber) will help isolating the floor from the cabinet vibration. But if the floor is already carpeted thick enough to isolate and damp vibrations, the only effect of the feet might be to stabilize the cabinet. In this latter case, connecting the cabinet solidly to the floor with hard spikes
can actually make it worse -- only experiments will tell. On the other hand, if the floor is very solid (such as those placed directly on a concrete slab - like in my house), then I do not think having the feet does not really make a big difference, besides stabilizing the speakers. If the floor is heavily carpeted, it can indeed make the speaker less physically stable; but I do not think that will affct the sound quality.
Bottom line -- do experiment! After all, it is quasi-zero cost...
Cheers!
