Stop by your local granite shop (could be to the gravestone maker himself)and ask for 3cm thick remnants, which are usually no to little charge. Purchase simple rubber / soft plastic, self-stick bumpers at your local or big box hardware store (the kind of bumpers often used on kitchen cabinetry doors). Apply the bumpers to an appropriately sized granite slab and place atop and beneath your speakers, atop and beneath your equipment. Experiment with this simple idea and you may be surprised how much this helps isolate components and clean up the sound for basically no cost. And if you find the right remnants they will look killer with your gear.