Oops. I had replied to this until I saw its parent was nearly 3 years old. So as I don't (quite) waste the typing:

Do you believe, as you sit there with the two boxes in front of you, that their contents are fixed?

Yes.

That there is a "fact of the matter" as to whether box B is empty or not?

Yes.

Or is box B in a sort of intermediate state, halfway between empty and full?

No.

If so, do you generally consider that things momentarily out of sight may literally change their physical states into something indeterminate?

No.

Do you picture box B literally becoming empty and full as you change your opinion back and forth?

If not, if you think box B is definitely either full or empty and there is no unusual physical state describing the contents of that box, then would you agree that nothing you do now can change the contents of the box?

Yes.

And if so, then taking the additional box cannot reduce what you get in box B.

No, it can't. (But it already did.)

If I take both boxes how much money do I get? $1,000

If I take one box how much money do I get? $10,000,000 (or whatever it was instantiated to.)

It seems that my questions were more useful than yours. Perhaps Joyce beffudled you? It could be that he missed something. (Apart from counter-factual $9,999,000.)

I responded to all your questions with the answers you intended to make the point that I don't believe those responses are at all incompatible with making the decision that earns you lots and lots of money.