Prima donnas? You misunderstand the nature of 9's. It's not about status, it's about waste. If you waste their time with repetitive work they could eliminate with automation, they resent it. Give them the responsibility AND the authority. Demand that the work be done, but don't set capricious requirements on the how. You'll rarely be disappointed.
As for documentation, 9's document for other 9's and other 9's have little trouble following the work. A 7 can't always follow a 9's thinking well enough to change the code, even when you luck out with a particularly good communicator.
If you follow your approach, you'll have high turnover with any 9's you manage to hire. You don't offer them anyone to learn from and you force them to dumb down every good idea they have. That's why google only hires 9's -- they can't afford not to.