Warrenh & Theaudiotweak, sorry but you may have missed the point. The sand/lead, in this instance, is for mass loading, not "vibration absorption." (Yes Warrenh, I did read your review). The Target R2s are filled with sand or lead, thus creating a v.v. heavy object. The speakers don't sit on the sand (situations where sand as used to absorb energy), but rather on the metal top plate of the stand itself. The blu-tac is used to effectively couple your speakers to a heavy object--also *not* energy absorption. Frankly, I'd bet dollars to donuts that the ProAcs would sound better epoxied to the R2s, only that really messes with your resale value. Blu-tac is simply a removable substitute for glue.
Here's the real issue. When a speaker cone moves back and forth, it displaces air, and, on an ideally frictionless surface, would result in the whole speaker cabinet moving back and forth. As a practical matter, we don't put speakers on frictionless surfaces, but, notwithstanding that, there is some movement back and forth opposite to the cone movement; at a minimum, this damps the acoustic wave that travels to you.
You *cannot* minimize this by decoupling. If the cabinet is left free to resonate, the damping will occur. You *can* minimize this by making the energy required to move the cabinet so far in excess of what the displaced air is capable of moving that the movement is minimized. This is the theory behind spikes, cones, heavy speaker stands, and the blu-tac. You couple the speaker with blu-tac to the stand. You make the stand heavy--that way the speaker and stand act as one. To the extent possible, you try to couple the stands to the planet Earth with spikes. That makes it even more immoveable.