ok, fair enough - I suppose I was overcomplicating things - but the sorbothane layer will squish less on top of isoacoustics as it would on a solid surface, no?

let's say the rubbery bits in the isoacoustics take 40% of the squash (ie the force of gravity pulling the speaker towards the planet), does that mean your sorbothane is much less loaded than you calulated...??

That might change its ability to 'do its thing', no?

Also where the original posts were simply mass(speaker) >> spring(sorbothane) >> mass (heavy stand)
now we have:
Mass(speaker) >>spring(sorbothane) >> spring(iso-topcup)>>>>small mass(iso-leg)>>spring(isobottomcup)>>large mass(heavy stand)..
The isoacoustics actual layer of rubbery stuff seems (vertically) pretty thin between the rim/end of the metal leg and the outer flat of the 'cup' under pressure,it's pretty soft, though. At a guess that won't decouple very low frequencies. So perhaps the benefits of sorbothane still shine through..

anyway luckily, it seems your experience is that it 'just works' - because who knows what the theory would have about that lot!