I've spent a good, solid, two weeks listening to the Eikon (Padauk) via my Oppo HA-1 and I'm mightily impressed. For its balance of frequency response and technicalities I'm not sure it has any major competitors out there regardless of price point. What I mean is that you can find headphones with better technical aspects--better speed/transients, soundstage, detail, tactility, dynamics, distortion, imaging, image size etc.--but most of those headphones will suffer in another technical area or will suffer from a wonky frequency response. There aren't many headphones that seem to excel in ALL of these areas. About the worst thing I can say about the Eikon is that it's a Jack of all Trades; that I really can't think of anything that it's genuinely weak at, even if I can't think of anything I'd call it the absolute best at. This would make a fantastic choice for anyone looking to scale their listening down to one "do-it-all" headphone.
Regarding frequency response, Eikon is about as close to ideal as I've found since I sold my beloved R10s. Literally the ONLY fault I can find with it is a slight recession in the upper mids, roughly from 2k-4k. This is the only area where I think it can potentially lose to the HD600s/650s. I say "potentially" because with any poorly recorded music that stresses this region--and it's pretty common to do so in modern pop/rock--I actually think the Eikon's slight recession would be preferable. However, I do notice it being a negative on well recorded music that makes use of these frequencies to enrich the tonality of instruments: eg, female vocals, trumpets, violins. The slight recession can make those instruments seem slightly hollow in that you hear the fundamentals and lower treble more. So I used my Equilibrium EQ plugin for JRiver with this setting: Gain: 2.5db - Freq: 2250 - Q: 1.5 to boost them. It's not quite right to my ears (would be nice if Tyll would produce some measurements), but it's close. Perhaps if I'm nit-picking I could also say the treble isn't quite as smooth as the 600/650 either, but it's far superior to any of the Orthos I've heard.
For sheer listenability, this may be my current favorite headphone. I also currently own the HD800S, LCD-X, HE-6, HD650s, and HP50s--which are basically the only ones I've cared to keep. All of them have significant flaws that the Eikon doesn't have: HD800S still seems to bright and bass-light; LCD-X has wonky treble; HE-6 is also quite bright; HD650s lack bass and soundstage. They also have a few areas where they're better: HD800s soundstage/imaging & clarity; LCD-Xs bass and tactility; HE-6s speed, detail, and punch; HD650s upper-mids/treble. But, again, it seems to me that the other headphones' flaws are more significant than those of the Eikon, which aren't so much "flaws" as areas where it's merely "good" as opposed to "excellent." Much like with my R10s, I tend to think that these kinds of "do it all well" headphones are more viable long term than headphones that have a few areas where they excel, because the latter's flaws tend to grate more over time as their impressive elements lose their initial "wow" factor. I think Eikon is a headphone that will be very difficult to grow bored of, while it's probably a very easy headphone to fall in love with long-term. IE, a better "long term relationship" headphone than a "short, lustful fling" headphone.
So, yeah, well-done Zach. You managed to impress a pretty jaded/cynical audiophile like myself, and apparently many others.
PS, I also have the Atticus in Cherry, but I haven't gotten around to listening to it yet. I prefer to take time to get to know one headphone before comparing it with another.
PSS, I'm less picky about sources/amps than some. My general view is that amps that can produce enough clean power will sound practically identical, or enough so not to worry about minute differences. With my HA-1 I generally have it cranked almost to 100% ("+6") on the "Normal" Gain channel, but that's because most of what I listen to is high-dynamic classical and jazz recorded at a low-level to maintain dynamics. I'm guessing anyone listening to modern music mastered louder would have it at -6 or less, unless they listen much louder than myself.