Reporting back to say I returned the Unions to Zu. They do improve with break in and did a lot of good things, but they were for a third system (I know). For the record I have Zu Defheads in my bedroom that I've listened to daily for the last 7 years.
I've had about 5 Zu models in my home and the funny thing is they all sound different. The Unions had crazy transient repsonse and were easily the most sensitive Zu speaker I've heard, I'd be surprised if they did not measure close to spec. The new internal Griewe scheme works well. However they are also the most unforgiving of recordings of any Zu model I've had, and I like to listen fairly loud. It's easy to hear the performance gains played side by side with Dirty Weekends, but I don't listen to much female vocals, and there's no question the DW's are easier to live with.
I did have a buddy come over and listen who has heard all of my Zus, and he said he liked the Union 6 better than all of them save for my Defheads. Better than DW, even better than Druid V. I don't share that opinion, I liked Druid V more, but I mention it to point out as always YMMV. Also I was playing some Brazilian music while he was here which was right in the Union 6's wheelhouse.
Anyway, definitely worth an audition and that's why Zu offers their generous trial period.