Spikes or rubber feet.

@gphill 

I called Aerial and talked to Michael Kelly about this very issue. He recommended that I use the spikes since my floor was not a slab but a floor with joists over a basement.

Interesting since it is usually the other way around.  Decoupling typically sounds better over a suspended floor (i.e., over wood joists).     As some have mentioned, Herbies makes some decoupling products.  If I still had my system set up on the upper level of our house, I would consider trying these, which came up recently in another thread.
http://avroomservice.com/evp-2/

I have owned two different types of Aerial speakers and in both cases used Sound Anchor stands to increase the weight and improve stability (i.e, the stands extend out wider than the speaker base).  You could used either spikes or decoupling materials below the SA stands.

Find out what gauge thread the inserts in your speakers use, and then buy some Herbie's threaded gliders.

I prefer the rubber feet. They decouple the speakers from the floor. Also, they are far less hassle.

If you hear tremendous differences between USB cables (for example), you have golden ears and should try the spikes. Otherwise, just enjoy your speakers (and unmarred floors) the way they are.