I'd guess that even a movie, made by AI using nothing but a book you paid for, would still be okay for personal use. Again, we already have the right to hire an entire theater troop to come to our homes and perform whatever we want. As long as you weren't making your AI movie commercially available you'd probably be alright, that kind of thing might be transformative enough to be covered under fair use, although I'm guessing somebody would still object to you posting it online for free.
Honestly, if AI ever gets good enough at crafting films from literary source material that the AI movies has any chance of competing with a hollywood production the entertainment industry is screwed. I'm positive that by then whatever crazy stuff that AI is putting out will be everywhere and playing with it would be way more fun than a movie theater ticket.
Different voices would be cool, but who is speaking which line can sometimes be ambiguous even for human readers. I'd be happy with just one voice that didn't sound like a robot or like a human voice spliced together from multiple sources.