I have two ways to go, powder coat or black anodizing. The interesting thing is what each would do to the grills. The powder would likely make them less resonant, the anodizing will probably make them ring more due to hardening. Powder will be matt, anodizing will be shiny. It's a toughie.
As long as the powder is not spooned on it shouldn't make too much of a difference to size, anodizing may make them a little brittle due to how fine the mesh is. I'm currently thinking powder coat at this point.