I polished my RX-5000 platter with MAAS and the supplied cloth. I also investigated metal shops around town which dealt with hot rods and motorcycles for polishing up chrome or stainless. I feared that gunmetal being a softer material would ultimately warp if not careful and the guys at one shop I emailed, I had to explain what gunmetal even was, so decided to just do it myself.
That said I was able to get a really nice shine on the platter, but has since patina'd quite a bit. I seem to recall that Micro applied some type of coating on these platters that if removed and polished, it will patina quicker.