Ren, go read the article. He specifically says "six layers of 3/4" plywood, plus a floor joist over 2" thick". Not exactly in those words but close enough. He did not say "one layer of 3/4", 6-ply plywood". Besides, it wouldn't make much difference. Just for shits and grins I'll also do the 6-ply plus a standard 2x12 floor joist. I'll be surprised if a slug goes through that, either.

My pics will be out later- if not elsewhere, then here.