Our club uses an angle grinder that we modified with a water feed with diamond wet-sanding marble/countertop discs at varying grits (similar to https://www.amazon.com/ADVcer-15pcs-Diamond-Polishing-Pads/dp/B07BVVHBJG). We've got a clever splash shield for using it in that has an adjustable bracket for holding the stone in place. You can get a high polish on a flat stone in a few hours.