OK i also agree if they want a realistic portrail of Cyrus and the Achamanids they need to cast people who at least look something like Persians. I think the movie if not made by the guys you are talking about will be made eventually some time in the near future hopefully.
Another thing not having to do with this subject is how do we know how the Persians lived there is little written evidence to tell us of there customs not counting Nowruz or other ancient holidays. I think it would be very difficult to make a movie about the Persians and Cyrus with out these facts.
I personally have read several books on Cyrus but most of them were fictional creations telling about his child hood. So you see it would be very hard to tell the story. With Alexander on the other hand and the ancient Greeks they had so much written facts and evidence of thier daily lives and about Alexander's personality as well.
These things are missing about Cyrus and the Persians so that is what i am basicly trying to say.