I own both 800S and Arya Stealth.

I'm gonna be honest... I slightly prefer 800S. They just sound incredible. And it's not just the insane Soundstage (though that's part of it), they're just tuned really well, I can head perfect separation and while I thought the light bass would be an issue, it actually makes some songs sound even better, like Linkin Park - Numb. On the Arya, the bass bleeds over but on the 800S, it just sounds right.

They're also way more comfy. Though I did mod my Arya by adding 3 Dekoni nuggets to the headband and put a cloth button-up cover around the headband and nuggets to keep them from falling off. It's comfy now, but stock hurt my head. Senns are still most comfy though.

I love both headphones though. Arya just sounds slightly more forward with female vocals that really makes them shine. But if I had to choose... I'd go with the 800S. They're also WAY better for gaming.