How do you reduce floor sound transmission?
Here's what we've done so far. I'm curious whether there may be better techniques...


R-19 batts between joists to reduce noise transmission through air
liquid nails on top of joists to reduce squeeking subfloor
first layer of 1/2 inch plywood
"green glue", a gummy substance to reduce foot fall noise transmission 
second layer of 1/2 inch plywood
rosin paper
hardwood planks


Actually we haven't installed the hardwood floor yet but we tried walking around on the subfloor and talking in fairly loud voices and neither could be heard in the floor below. Adding another layer of wood should only help. 

One option that we skipped is to use joist isolators which are pads that go between the joists and the subfloor.

I've been told that there are three principles at play when trying to reduce sound transmission:


the denser the floor the better (ie concrete is better than wood)
the thicker the floor the better (ie 3 inches of wood is better than 1)
the fewer (and softer?) the points of contact between floor and ceiling the better (eg green glue and joist isolators)


The first two are pretty clear. One example of the third is if the ceiling below is dropped and does not use the joists above for support. Instead the ceiling uses only the walls on either side, and ideally the wall studs aren't connected to the joists either.