What should be under my speakers?

I have Sonus Faber Grand Piano Home speakers in a 20' x 17' room with wood floors. The speakers have spike feet, and each one is sitting on a 1 inch thick, 12" x 12" slab of granite. Each piece of granite has a square piece of carpeting under it, as a further buffer. I know I probably could figure this out with a lot of experimentation, but what impact is the carpet likely having on sound quality? Would it be better (Subjective, I know) to have the granite slabs sitting directly on the wood floors? How would the sound change if I ditched BOTH the carpet and the granite? I would like to maximize bass impact, because these speakers are a bit thin in that regard. Thanks.