What do you put underneath floorstanding speakers?

I have a wood floor with a basement underneath. I minimize floor vibrations by placing my speakers underneath a patio block that I have spray painted. I think you can use granite underneath for a more elegant solution.

to reduce the sound in the appartment bellow you should do a sound proofing.
placing a carpet in the entire room where the stereo system is located will partially solve your problem.
you may than use platforms that you would place on the carpet under the spiked speakers.
marble platforms tend to kill resonance most efficiently but are not cost efficient so you could stay with MDF ones.

Star Sound Technologies. I tried their Audiopoints first and what a differnce. The soundstage increased in height and depth. I have since then moved up the food chain and purchased their Sistrum Sp-1 to go under my speakers. I have not received them yet but I will comment when I do. They offer a 30-day money back. This has been my experience and I am sure you will get other ideas. Whatever you choose I would encourage you to hear it in your system to determine if it is a right fit.