Both Zu and Spatial make high efficiency high impedance speakers. I have a horn-loaded single driver speaker system as well and have heard a couple of mid-line Zu speakers and in both cases, almost regardless of the pairing amps - tube, SS, low or high watt, they all sound somewhat congested at higher volumes playing complex orchestral music content, As much as they excel in imaging while playing more intimate musical genres, they don't seem to be suited for rock and/or western orchestral classical music. Just my experience.
Speakers for First Watt SIT-1 amp
My favorite sound seems to come from an SET amp and single-driver speakers but I want to leave the amp on all the time and I have kids in the house so I decided to exclude output tubes. I went on a hunt for a solid state amp with an SET sound and landed on the First Watt SIT-1 monoblocks which I love. I'm using them with Omega Super Alnico High Output monitors and it's a great combo but I wonder how much better speakers like this can get with this amp. I have my eye on Voxativ, Teresonic, Audience, and maybe Audio Note or Daedalus. Any suggestions?