underlayment for floating engineered wood in basement w/ subslab VB

last month

Finishing off the basement, and I'm planning to put a floating engineered hardwood floor in a good portion of the new living space. The house is only a few years old, concrete floor is nice and level, and - here's the part where I'm finding a lack of information - there is already a vapor barrier in place under the slab. I'm trying to end up with a total flooring height above the concrete of 3/4"-7/8" in order to match up with other flooring, and want to use 1/2" - 5/8" flooring, so I have 1/4"-3/8" of height available for underlayment. My original thought was DMX 1-step (5/32") + 3mm cork, but is the DMX overkill if there is already a vapor barrier? I see the frequent recommendation of 6 mil poly + 1/4" cork, but is it bad (or unnecessary) to add an additional vapor barrier? Can I place 1/4" of cork underlayment directly on the concrete, since I have the subslab vapor barrier?

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