Changing gloss marble finish to honed finish
Typically a honed finish is done with 400G as a finished cut. Since the marble is much softer than granite which the 400G would only rub over it, without cutting at all, you would need to start with 50G to start the process with granite. With marble you may only need to it it with the 400G and call it done. If that resists the 40G cutting it, you may need to stat with a much coarser cut.

The vinegar trick in the article referred to will literally eat the surface gloss off the marble,unless it is sealed. Vinegar is a very mild acid, but it will attack the softer portions of surface and remove more than other portions. IMO, the 400G sanding will keep the surface more uniform, if the sanding is done in a uniform fashion.