I use large floorstanders, and although it's a project I've yet to get around to, I've had plans for years to build plinths to support them which incorporate the key design features of the monitor supports you've linked- namely provision for height/tilt adjustment and mass/damping layers. The combination of a mass layer suspended between damping layers is "constrained layer damping", based around a layered construction with a flexible damping layers on either side of a more massive layer 'suspended' between them like a sandwich. It's a common and effective strategy for vibration damping and noise-transmission reduction products like generator housing and engine room wall linings which are similar in construction to the isolation product material Jon lined his soffits with.
If you look at the design of the monitor supports linked above, you'll see a similar idea with a mass layer suspened between flexible layers. In that case it's a rigid plate to help keep the monitor stable, but it's the mass rather than the rigidity which works to help damp vibration transmission.
In my yet to be realized design I'll have a Sorbathane layer (a flexible polyurethane with excellent damping properties) between two heavy stone or concrete slabs, with threaded legs embeded in the top slab which rigidly connect the speaker enclosure to the slab and allow for tilt adjustment and somthing like upside down carpet adheared to the underside of the bottom slab to allow me to reposition the speakers around on my hardwood floor more easily as required. It's been on hold for like 5 years,
but I've not been supermotivated to move ahead with it since I can use them as they are and the entire house need lots of other more important work first.