Be careful of designations and fancy products on the market MIC 6 is just a registered brand name that has a superb flatness, finish and parallelism. Usually when you build a machine you correct these errors by adjusting or compensating. Unless you have an unlimited budget, milling the plates flat yourself. This shouldn’t be a problem with any convention mill.
You need to consider also the mechanical properties of the aluminum for example construction aluminum is good for building because it is elastic and is more forgiving but a real disaster for milling. i have never had much luck with it. I prefer any avionic type alu because it just "feels" better, its lightweight and can be easily milled