I've been enjoying my Atrium for almost two weeks now and wanted to share some brief impressions. It has quickly become my favorite pair of headphones, right up there with the Vérité Closed, and made me even consider perhaps downsizing my collection and selling my VO and LCD-4!
The biggest positives for me are: A) The Soundstage & Separation of instruments. They are quite unlike anything I've heard from a Dynamic Driver headphone so far. I briefly had an HD800S, and not at the same time as the Atrium so can't compare them, but I didn't feel as impressed by those at the time. I think the main thing I recall then is the HD800S had a wide soundstage, but with the Atrium what impresses me is not how large the staging is, but how well-separated instruments are. Different parts of a song feel defined in their own space, and it's very easy to paint a picture of things in your mind. B) The Timbre. Instruments and voices feel extremely real, especially out of the ZMF Pendant SE amp - this coupled with the impressive separation means that you have a sense that you can almost reach out and touch the different aspects of a song! It's super realistic, and I'm in love with it all. All of that and it still maintains a significant amount of body and bass as well, without ever feeling muddled. What a fantastic headphone this is!
I mentioned this before as well, but 100H of burn-in definitely made a difference for me. Things sounded smoother, and the separation was more evident after the burn-in - though they sounded good at first still.
The one negative for my specific pair (and this is 100% preference-based): The aged copper grills are maybe
too aged? They look almost entirely gray, instead of copper. But again, just my own preference.