Before you can decide how to power them you need to know what particular units are you using. If they're drawing any sort of current you're going to have alot of issues with battery life! You're almost definitely better off using an external supply and, if you can, regulating the DC input to keep the noise down.
Tremelus Lune is the one most often quoted here, though there's probably simpler again. Still, if you're building a Phase 90 that should be no trouble. Try and make sure they take the same voltage or you're going to need 2 regulators.