Glue down the Serenity Mat to the original subfloor (could be a slab or wood frame). Then glue down a layer of 3/4″ Tongue & Groove OSB. OSB resists warping better than plywood.
Take care if the floor has valleys & crowns as the plywood may not lay flat. This may require a concrete Tapcon screw to be installed and later removed when the glue dries. You can set a bag of sand or heavy object as well.
Soundproofing Floor Solutions