Do you use spikes for tile/marbel floor?

4 pennies per speaker. This is the way to go.
Cheap and doesn't muck up the hardwood floor.

I have my spikes replaced with standard furniture glides from the hardware store. Meadowlark recommends this for their Kestrals, might work with your speakers as well. The thread size is common, 1/4 20. If this doesn't work Linn makes a product called "Skeets", hard metal discs with holes in the center for spikes. Hope this helps.

It depends. My Martin Logans prefer brass spikes into brass cups and my Thiels prefer thin nylon washers.

Replace the spikes with Black Diamond Racing Cones. The BDR cones will not harm your floor and will allow your speakers to reach their full potential.

I prefer to use a brass coupling disk that can be found at: audiopoints.com mine have worked great on hard wood floors, concrete, and the bottom side of my stereo components where the point of a spike meets the bottom of the equipment.