If you watched my review, I mention the HD800 vs. Atrium, briefly. Essentially the HD800 seems to have a consistently wider stage, but it sounds artificial to my ears, njot mention the peaks and anemic sound in general.
The Atrium indeed has a massive stage in all directions, and depending upon the track the width, is at times, breathtaking.
I'm getting a slightly wider stage via the Wells Dragon lvl 3 than I was on
my @robo24 GOTL. The height( and below the stage ) is about even on both amps, but the depth is much more pronounced on the GOTL.
If you're looking for the absolute widest stage in history than an estat might be your ticket. However, like I said in my review, the combination of bass, mids, texture, musicality, imaging & tonality,
in addition to the staging, I do not know of another headphone that offers that magnificent combination other than the Atrium.