I highly doubt the Eikon, or any ZMF headphone, will have HD800 like treble presence. Zach tunes around linear, but very smooth sounding treble. I'd say his treble preferences are a bit more forward than the HD650, but not by a lot. Definitely more smooth than the HD800's aggressive treble. The Eikon should be an excellent compliment to the HD800, in my opinion. Smoother, much more intimate in soundstage, a bit more warm, but still fast and clean. Seems like a perfect duo to me. That's an interesting question that I had not even thought of.