A related but not direct answer - I find that much depends on what speakers you have, and what they are made of, and how heavy they are to begin with. For 'light' speakers, like Harbeth (comparatively), people use bluetack - which by the way can stick to the veneer and tear it off - which maintains the box-portion of the speakers' contribution to the music, without over-damping it. While other speakers, perhaps heavier or with thicker walls, benefit from more solid damping. I think there is much trial and error there. But what I do know, is that for this second class of speakers (heavier), adding significant weight on top of them can make a huge difference. It looks ugly, depending on what you use. Otherwise, whatever cone, puck, or magic tool you use UNDER the speaker is only a function of how heavy the speaker is (and how much mass is connecting the 'cone or puck' with the speaker and stand or floor). Yes, general statement, I'm sure with many exceptions, but worth trying out.
As an example, have you seen pictures of nice looking monitors atop heavy brass cones atop heavy maple or wood plinths? That would be a good example of doing everything possible at the bottom end of the speaker to benfit the sound and preserve the 'looks' of the speaker. I would bet that if a 10-lb brick were place atop the speaker (say with some simple cork or rubber as a buffer), and simple spikes at the bottom, then more would be achieved for the sound. Otherwise, the speaker, atop whichever monstrosity is placed below it, still relies on its own cabinet construction, gravity, and moving parts (cones) fighting the cabinet, to produce the sound.
I suppose a good illustration of the ideal would be to have a concrete wall with drivers in it (and obviously whatever internal space required). Like Green Mountain speakers in fake concrete, Aerial 10T's and B&W matrix/nautilus midranges in man-made concrete, etc. Since everyone has not done this, then obviously there is a desired interaction in the driver-cabinet interface. So now, we're back to Harbeth's and the like. But I think that illustrates the point I'm trying to make.
