> Well the density goes down the larger the black hole so the extra states are still missing.

Huh? If the correlation between density and mass is perfect, that means two things:

1. There is an upper limit on the mass of the black hole, set by the volume of the box containing it.

2. The black hole's possible mass and density occupy a one-dimensional space and not a two-dimensional space.

Now, it appears to be true that the (possibly nonlinear) correlation between mass and density is perfect; for any mass a black hole can have only one density. But that doesn't make the space of possibilities finite. It certainly won't make it into a single point. And in fact black holes appear to have three independent physical dimensions: their mass, their electric charge, and their spin.