Floor Resonance and Full Range Speaker Stands

I'm also in NYC and, in the process of moving, looking to bother the new neighbors as little as possible (just think, could be coming to a building near you...). For the past two years, I've had no downstairs neighbors, thrown the Thiels on spikes, and let'em rip without consequence. Now, I'd like to decouple the speakers from the floor as much as possible (to transfer as little sound as possible downstairs). Is granite blocks the best way to do this? In spare moments, I'd dreampt up all sorts of theoretical, layered isolation configurations and such, but am only guessing. If we're talking granit (or some similar, rock-like stuff) how much of a slab would one need to do the trick? HxWxD, approximately? The more the better? Finally, since I'm playing 20 questions, where would one find a slab of granite? I'm not talking designer acroutrements, just the basic hunk of rock variety. Thanks.

Set the granite on some inflated bicycle inner tubes and set the speakers on them.

Concrete slabs may "ring" while granite can absorb -- so probably better. I beleive the best solution would be to use granite sized slightly larger than your speakers, and decouple the granite from the floor with the likes of Audiopros or even cheaper devices such as Nordost's Pulsar Points.

Good luck!