I have not been able to play these 24x7 as I've had family working to pack up my house during most days (and they didn't want to listen to music, apparently), and so I'm guessing I maybe only have 30 hours or so on them so far.
At 20 hours or so, I felt like maybe tonally the speakers were tilted just slightly toward the upper registry at that part of the break-in. I didn't feel like I was hearing the same midrange growl and oomph that I was used to from the full-range drivers in their speakers. Piano strikes felt a little thin, maybe? Maybe? It wasn't bright or biting, but voices maybe just felt a tiny bit tilted upward tonally. Total speculation but maybe the two drivers were burning in at slightly different paces.
10 hours more now and I feel like it's coming back into the Zu balance you would want/expect (assuming you're buying the Zus for that particular balance). As mentioned previously, the hints of pinpoint "hi-fi" sound are totally gone thank goodness, but they are definitely even more detailed than my Soul Supremes.
The soundstage is physically taller than the one produced by my Soul Supremes, which is to be expected given their physical height differences. It feels natural, not exaggerated. It's still maybe a little more forward than I would ultimately prefer in my small 11' wide room, but that has moved back (improved) with time, so maybe it will continue with further burn-in.
Probably the biggest single difference, aside from detail, that I'm hearing between the SS's and the Druid VIs is the amount of decay. The VIs are seeming to have an even blacker background that it really allowing a nice, natural decay...to a degree I haven't had before.
As the break-in continues, I'll turn the Undtertone off and try to get a feel for the low-end and report on that.