On S2 or Luna, what is the final finish for "natural" cabinets? Is it some sort of oil? I'm wondering about the possibility of darkening them with a rub-in or rub-on stain, in case of a change of installation in the future. That would not be easy starting with a lacquer or polyurethane coat, without removing at least the drivers (back is less important). I would not do 'paint'. Thanks.