With the update of 17th October iMovie can now export ProRes 422, it can also import ProRes 422 files and edit them without having to convert to the old AIC codec.
To import a ProRes file into iMovie from say, a Canon DSLR, first convert it from Canon .MOV to ProRes and then import to iMovie. Excellent quality. There are many file converters available but I would recommend Toast 12 Pro.
