Given the high sensitivity, it is essential that you have an amp that is ultra-quiet and Art Audio is designed to work well with Avantgarde at 104-107dB sensitivities.
Art Audio is an awesome match for Zu. WIth 101 dB sensitivity, most SETs will do the job and do well. I have had customers with Druids run but our 845 (Carissa) and 300B (Diavolo and Harmony Silver) power amps and have tremendous results.
If you are looking for a more traditional integrated, an ideal option would be the Canor AI1.10. Again, have a customer who has Tektons, Zus and Cubes and this sounded great with all three.
I am the importer for both brands. Obviously I am biased, but in the same token I do have lots of customers and Zu is a common pairing for those customers.