I have a custom made pair of Symposium Svelte shelves on my Verity Audio Parsifal Encore's that seperate the bass module from the mid/high module. They replaced the standard granite slabs.
If the speaker has enough weight they work great on carpet if its not too thick, even better on hardwood floor. If there are any spike inserts should remove them so the entire base rests on the Svelte so it can absorb the energy from the cabinet. I have used them on Proacs 55lbs, Spendors 100lbs and Sonatinas 65lbs with great results. Drains the resonance energy away from the speaker much better than spikes when used under the right conditions. Peter at Symposium is a good guy, check with him.
The Quatro's are around 115lbs. We used two short coupler's in the front two spike recesses' and utilized the rear spike without washer's and placed on a dime(which BTW, bent from the increased pressure. I think he'll try the steel plates).
What do you think of Rollerblocks under speaker's(he's a bachelor)?