Just another shout out for the Atticus. Such an easy, detailed, full, rich, warm yet dynamic/punchy sound (paired with my OTL Woo WA2). If people are looking for, say, an upgrade to the HD650 (as was mentioned), this is it. Or what I'd recommend at least.
Sticking with the Sennheiser parallel, the Eikon on the other hand is more like playing in the HD800 territory (no not as transparent and spacious, but like the HD800 it is more linear and perhaps a touch more detailed than the Atticus). As with the HD800 though, people with treble sensitivities be advised: the Eikon can run a bit hot up top, as has been mentioned before. It also does not sound as full or rich or 'present' to my ears, compared to the Atticus. It has a distant quality in its presentation that makes me keep wanting to turn it up, only to aggravate my treble sensitivity. Those concerns aside, I do think it is otherwise a lovely headphone, and I'm sure for some it would be just right (for instance, someone like Tyll Hertsens saying how much better he thought the Eikon was. Go figure. That still takes me aback).