On paper I don't see what would make the Gryphon Diablo a particularly good match with the Nenuphar given the specific design objective of this speaker. However as has been shown before there's no substitute for actually listening and judging.
I don't know why granite would necessarily be superior to the original Nenuphar cabinet. This is a very well thought out cabinet to match the superb driver and no doubt is a major factor in the overall sound quality.
Charles