I found Atrium Open to be darker, richer, much more mid-bassy, but smoother and softer. MUCH thicker sounding, if that’s your thing. The soundstage is actually pretty similar - maybe HD800S is a bit wider. Treble on the Atrium is more rolled off, if you find the HD800S too bright.
Verites (had Open, still have Closed) are just about as fast and detailed as HD800, maybe more so actually. As extended top to bottom, with a slightly richer sound. There’s more of a 3d effect to the soundstage, like you’re on stage surrounded by musicians. I found the Senns to be a wider stage, but it’s more spread out in front of you, like you’re sitting a few rows back. I think there’s slightly more textural information in the Verite, you can hear more rosin on the bow as it were - but both Senn and Verite are great at that.
Verite and HD800 are actually kind of similar to me, but Senn is the light side and ZMF is the dark side. In terms of musical enjoyment, Atrium is great for electrified stuff, classic rock and the like. Verite and HD800S cover similar genres, anything acoustic. HD800S is the best I’ve heard for orchestral, but Verite produces the best violin I’ve heard. Verite does a little better with harder genres like speedy abrasive metal.
Hopefully that helps. This post ended up being…a lot longer than I expected