While I don’t have first-hand experience with the Silver Dart I’m currently using Zavfino speaker (Prima Mk. 2) and power (Prima Mk. 2 and Fina) cables in my system--and I really enjoy the them. If you have questions about the Silver Dart cables, you should email Ray (the owner of Zavfino), he responds quickly, is a straight shooter and very nice guy. He gave me objective advice when I was purchasing.
As others have suggested, Acoustic Zen Absolute are a fantastic match for Harbeth. I’ve owned the Absolute (which I used with SHL5+), they had such an organic and welcoming sound. To my ears, I find the AZ and Zavfino to have a lot of similar sonic characteristics.