I am planning to install a 3 1/4 wide X 3/4 thick wood floor. Have not decided on species. My question pertains to my subfloor. I have 23/32 Sturdifloor tongue and groove plywood subfloor, 24 oc joists. The joists are engineered approx 2x12 with cripple studs in between, criss crossed like this XXXXX. The joist span runs about 13 feet.

DO I NEED TO REINFORCE THIS FLOOR WITH PLYWOOD? If so, how thick? Or am I good to go as long as I go opposite direction of joists.

It will meet up to a tile floor that had to be reinforced with 1/2 inch ply plus all tile materials. So if I put the 3/4 wood floor it will still be lower that my tile. Basically, Height is not a concern if I need to add more reinforcement? Thanks you.

24" OC is the maximum span for 23/32 SturdiFloor. And you will notice some deflection and maybe a slight dip between your trusses. IMO, this does not meet the minumum requirements fo a 3/4" nailed down floor. To be on the safe side, I would add some more CDX plywood to stiffen your subfloor up. 3/8" should be adequate but 1/2" is better. BTW, your "joists" are called web trusses. An ingenius design that allows heat ducts and plumbing to be run easily without sacraficing structural integrity. Web trusses have been used for many decades in industrial construction but were most often made from steel.