Floor speakers on tile floors?

I had a similar problem--floor standing speakers on a hardwood floor produced some boominess. I sandwiched four Vibrapods betweem the floor and a piece of hard laminate tile, then set the speaker on the tile. That eliminated the boominess, tightened the bass. For visual aesthetics, it helps to have the tile no larger than the base of the speaker.

On the tile floor is not a problem. The easier to resolve the problem is to get some spike bases (shoes) for the spikes. In this way, the spikes won't be moved by the vibration and you can even get better resolution this way.

We've experimented quite a lot here in Zurich with various speakers placed on various materials with or without cones. One experiment we tried, was to place the speakers on cones, with small, one square inch tiles of very hard ceramic between the cones and a travertine floor. This we found the best solution to get the most air into the soundspace, to clear up muddyness in the low end and to get sparkling, peppy highs. One caveat though: Bad Cd's sounded worse in the highs in this form of placement. We were all amazed at the differences in speaker performance, whether we used a granite, marble, or travertine base, with or without those little pieces of hard burnt ceramic, which made quite a difference by themselves, in sort of clearing up the air, giving the musical rendering more bloom. This arrangement moreover, practically worked with all speakers, we tried it with. If I were you, I would start off with something like that and see if I liked it. Just my 2cents.