"Engineered wood"
ick
"over 2 layers of OSB"
What's that?
"vers over a rubber pad"
sounds good
"and Nail it or float it?"
Wouldn't nails restrict the movement you put the pad in there to allow?
From what I've heard, the state of the art is clips which attach the boards to each other, while leaving the whole assembly floating with respect to the subfloor. Remember the gap around the edge so you don't get bulging "ridgelines" from expansion.