My earlier response was written without having read all the posts, my apologies...
Mine did take quite a while to break-in, and it went through some wild gyrations while doing so. It does keep getting better, and better, AND BETTER.
Allan is right on the mark about the Berning. It doesn't really have a "sound". What ever changes I make in my system, the Berning will highlight them, good or bad. I am in the middle of trying some new cables, so I can attest to fact that everything you do will have either a positive or negative effect on the ZH. Set up and synergy are everything! On a side note, I have found the Berning to be fantastically stable, and user friendly. Shes never uttered so much as a burp.
Well, I guess I am wearing my heart on my sleeve here, but I really think is a great real-world amp.
Good luck
gb