I am currently installing a 3/8 solid. As a precaution I just applied MVP and plan to put 6mil plastic over that then 1/2" plywood down before nailing the floor. I also plan on laying 15# felt between the ply and floor, can I also lay felt between the plastic and the ply to really deaden the sound?
Any thoughts or experience on that??

Do you KNOW if you have a moisture problem with your concrete slab subfloor?. It would be worth it to check the moisture content before committing to these steps. And be sure whichever fasteners you use do NOT protrude through the plywood. What good is the plastic if you poke it full of holes? And how are you attaching it anyway? I would install the plywood while the mvp is wet, so it would be like an adhesive. Deaden the sound? If sound isolation is needed, then felt isn't going to cut it. You'll need cork or similar. I think you need to be more specific as to your goals before we can recommended the best way to install your floor.

Two layers (or more) of properly installed moisture barrier are no more effective than one layer.
One layer (or more) of punctured moisture barrier have the same effectiveness as none.
Sound-deadening must be accomplished with proper products, as Gary indicates.