The short answer is that there is not much horizontal motion in floors. Footfalls create vertical motion. Walls, of course, have motion on the horizontal axis, so here, you would want a damping action to work in that plane.
The racquet balls are working as a vertical damper. The stretching compliance of the balls works as the damper. Additionally, your slab is actually damped in horizontal action. The fact that if you push on the slab and it comes to rest quickly indicates you have dampened horizontal motion.
How this translates into improved sound is a different story. I've been tweaking for years and this is what I've experienced.
Disclaimer: There are some newer devices I haven't tried. With the exception of the CD player/transport tweak I recommend, there's also a lot of variation in results between different products even when using the same tweak, so experimentation is recommended.
Under CD players/transports:
Best results in order of effectiveness
1. Symposium Rollerblocks ($395) What I use. Don't ask me why it works since it only works in the horizontal plane.
2. Daruma III Isolation Devices ($99) What I recommend. 90% as effective as Symposium for 1/4 the cost.
3. A bicycle tire tube lightly inflated and placed under the platyer/transport. Schwinn tubes are readily avaialble and have very complaint rubber. ($5.00)
Both 1 and 2 have offered improvement no matter what player/t-port I used. Highly recommended.
Under DACs: Can't answer this one. I've experienced different results with different tweaks/DACs. My only answer is to experiment.
Under tube pre-amps: Lots of different results. Big time YMMV here.
1. Vibrapods, Isobearings.
2. DH cones. (better focus, but may tip the treble up a bit)
Under tube amps: Different results again. YMMV
1. DH Cones under the amp which is on top of a platform on top of a slightly inflated bike tire tube. My hypothesis here is that sub-sonic vibration (1-15 Hz), while not directly entering your system, may be causing some mechanical alteration to the operation of the tube.
Under solid state amps.
1. Cones usualy inmprove the focus, but depending on the material you are using, the treble may be tipped up or down. Ceramic cones tip up, composite cones may be a bit more neutral. YMMV
Under solid-state pre-amps- Never owned one, so I can't comment
Hope this helps.