In terms of sound signature, the 1266 has more presence in the upper mids - treble, a bit less warmth in the lower mids, bass quantity/extension is very similar. It has a bigger soundstage that appears more spherical in shape, feels like it's more surrounding compared to the Empyrean's more up-front soundstage layout. It has stronger dynamic slam/impact (macro-dynamics), and generally just a much greater sense of resolution down to nano-scale levels of detail. So yeah, in terms of sound quality, it's categorically better than the Empyrean no doubt.
But does that mean that you'll prefer the sound of the 1266 over the Empyrean? Not necessarily. Although fit/comfort with the 1266 is already enough reason for me to favor the Empyrean over the 1266, the sound is also not ideal for extensive multi-purpose usage. Yes, it's extremely resolving, it has a very intense and powerful sound, it's an absolute blast to listen to, like a rollercoaster ride. And this is why I prefer the sound of the Empyrean, because I don't want to ride a rollercoaster for 6+ hours a day. They are intense, and that extreme resolution and intensity resulted in feeling a sense of sensory overstimulation. Not physical listening fatigue, but my brain getting fatigued. The level of resolution it portrays is also something I don't really want to be exposed to with all of the music I listen to.
If I could justify paying such a high price for a secondary pair of headphones for short, occasional listening sessions, I would do it in a heartbeat. But for a pair of headphones for all-round extensive daily use, the Empyrean with it's laid-back, full-bodied and also highly enjoyable sound and superb comfort is just the obvious choice for me.
