After having them a couple of days now (I think it's been four, but don't quote me on that,) I thought I'd pass some more impressions before I get the Decware tomorrow and then my review on Friday.
The Eikon has grown on me quite a bit over the last few days. I still prefer the Atticus, however. But I'd equate the differences between the two as a "HD600 vs. HD650" kind of thing.
Let me explain:
I've found the Eikon to be more neutral than any of Zach's headphones, as I've said before. It has a touch of bass, however, but said bass extends well into the subbass regions. The Atticus also extends far into the subbass regions, but it has a mid-bass/lower mids boost that makes it a lot warmer overall. Due to the lower distortion, said warmth is pulled off quite well (unlike, let's say, the HD650 at times.)
The treble also extends quite a bit further than I thought it would on the Eikon. Interestingly enough, the Atticus also extends pretty far into the higher-treble regions. The difference, however, is this: The Atticus is more immediately apparent in the lower treble, and seems to sound more energetic because of that. The Eikon, however, has more of a presence in the upper-treble.
Once you get to the mids, it seems the big thing that stands out is the added warmth on the Atticus making the rest of the region thicker and (slightly) more forward. It isn't overly warm to the point of muddy, however. The Eikon, on the other hand, has much more integrated bass and seems to sorta coast on into its mids. Quite frankly, it reminds me of the mids on the HD800 (without the thin sound due to the tiny bit of warmth nor the dryness caused by the upper mids dip in the HD800.)
The upper-mids part is where things get interesting. The Atticus, due to how the 2-4Khz region sorta sets itself, ends up having a timbre similar (but not exactly the same...think of an "approximation" more than a mimicry) to the HD600 and HD650. You can sort of hear the same thing going on with the Eikon, but it is a lot more apparent with the Atticus. In fact, besides the added warmth (I like the combination of the mid-bass boost and low distortion,) I believe this is the reason I am so partial to the Atticus over the Eikon (I have a soft-spot for that damn Sennheiser 6x0 series.)
Luckily, a buddy on the Headphones discord chat is lending me his HD600 so I can confirm that's what I'm hearing. One of my favorite headphones was a modded HD650 for almost the timbre alone, so it is exciting to recognize the same kind of timbre in the Atticus (which does things a lot better than the HD650.)
Ah, one last thing on the sound. The speed difference between the two has become less obvious the more I've switched between them. The Eikon is still in the lead, of course, but the Atticus has less issues catching up with it than I thought it would.
All things considered, it looks like I'm probably ordering a Padauk Atticus around Christmas.