+1 on IsoAcoustics under your gear. Probably the easiest and most effective solution for any vibration issues your gear may be subject to. Next, I agree that if your rack is between the speakers it can contribute negatively to the sound. Consider yes, thick cloth but also short acoustic panels on the side and behind the rack itself. Also, given the angles, room treatment on the ceiling between the speaker and listener is always a great idea.
Improving a stone rack
Hi all, I have a large stone rack for my system, in beautiful granite, which works great for stability, but maybe not so good for other aspects of the sound. I wonder if it contributes to some treble ringing and harshness. I want to improve the sound, thinking of felt damping on the wall behind the rack, some form of cloth to cover the reflective surfaces of the shelves, and adhesive rubber type mats on the bottom of the stone shelves. Is this the way to go? Experience based advice is very welcome. My rack weighs a ton. It is not easy to compare to a wood or composite rack. I need advice on how to counter the sound problems of stone or similar polished surface shelf racks. I want to try this, before I consider a new rack or shelf arrangement.