I've owned both and heard them at the same time from the same gear. Beyond the tuning differences noted by
@Hifiearspeakers, here are some other points of comparison:
The Atrium's resolution is very good but a step behind the Vérité's. It’s perfectly acceptable, though – I didn’t feel as though I was missing out on anything – and, besides, the Atrium’s resolution almost doesn’t matter in that what sets these headphones apart is the engaging and pleasant overall experience they offer.
The Atrium isn’t as fast as the Vérité. There’s a softer way of presenting music. Part of this is the biocellulose driver. The Atrium has a slightly more gentle, rounded attack to the transient response than the Vérité, which is cleaner and snappier. Both headphones have lovely decay, though, with the Atrium I get the sense that notes linger for longer.
Macrodynamics are strong without being as dramatic as the Vérité’s. They’re perfectly satisfying, though.
The Vérité offers better, more precise imaging, with instrument localization being nice and specific. The Atrium, by contrast, is a tiny bit less distinct. Separation and layering also go to the Vérité but they’re still very good with the Atrium. There’s plenty of air and space around instruments and the overall presentation is entirely free of congestion.