Will the AV2's "record out" output work whilst using the digital inputs? ie. Can I listen to movies using headphones and a headphone amp hooked up to the record out. (I am using the Av2 as a surround sound processor and preamp, I do not own a separate preamp)

Try it and see.

In my experience it probably won't unless they've routed the DAC to the analog line outs (or something like that).

I know Denons don't.