I use plastic bags filled with sand under, between and on top of my source equipment.  A "sandbox" should help decouple speakers from the floor and have good results in some cases.  Others claim good results with opposite measures and spiked feet on speaker cabinets, for tight coupling.

This hobby is crazy because almost everything can affect sound quality.  Imagine all the tweaks we might employ if only we knew about them.  I wonder how many neurotics the Stereophile has created?

** To be used in a cat free home no doubt.