Erik asks some good questions, but only you can answer the question of whether you think Harbeth speakers will work with your NAD equipment.
If you're buying new, perhaps you could work with your dealer for a home demo or for you to bring your NAD gear to the store for a listen.
If you're buying new, maybe you could just buy a pair. If you then don't like how they sound with NAD, you could resell them for little or no loss or figure out how to get different electronics.
Good luck!