Is nihilism the logical extreme of atheism?

[genkaus]

I would argue that emergent properties would answer your objection.

That was addressed by this line.

...Nor can the brain, as a whole, can be broken down into smaller and smaller interpreters, each assigning meaning to lesser and lesser signs. Even the smallest sign requires an interpreter no matter how tiny. You cannot build something out of nothing.

It doesn't address that at all. The idea of emergent property is that it cannot be broken down or applied to smaller parts. Meaning, brain as a whole can be the interpreter without being broken down into smaller ones.

... and we are back to humans defining their own morals and meaning.

a.k.a. nihilism.

Not according to your definition.