Good questions! I have all the headphones you're discussing. AO, AC, BC, VC, CC (plus Atticus and Auteur).
First, I hear the VC as you do, great with high studio recording quality, slightly fatiguing and harsh up top with rock/metal (also my preferred genre). I adore my Bokeh and put it and the Atriums on the same level, enjoyment-wise. I'm treble sensitive with tinnitus in both ears, worst in my left. I run an R2R dac and tube amps (Aegis, Stratus, V8 OTL) exclusively.
First, the BC is insanely fun to listen to! Screw technical aspects, the BC just sucks you in and gets your head banging! The Atriums both have that same effect on me. The AO is a slightly more evenly tuned set, with a bit less bass quantity but more balanced upper mids/highs. Not dramatically different from the AC IMO, but you will notice it if swapping back and forth. That being said either is excellent, and with pad/mesh rolling you can get either to sound much more neutral or warm.
Now the really hard question is does having a BC make the AC redundant... that's tough and so subjective. I have both and enjoy them equally. Yes they sound similar, but there's no mistaking one from the other. The AC (stock lambskin pads) is darker, with smoother highs, and more emphasis down low. It is more resolving than the BC, and more expansive sounding. Rolling the stock suede pads in will flip the signature and make it more upper mid focused. Totally different experience with suede pads. I prefer the darker lamb pads myself. It's thunderous! Much like the BC, it hits hard, digs low, and has a visceral bass response. The BC has a more even tuning in comparison. The upper mids/treble are a bit more forward and prominent (using protein pads and radial mesh, my preferred setup). Not fatiguing, but definitely more forward and present. The AC brings the low end more into focus, the BC more vocals/guitars. Both are metal monsters IMO. As for the AO, it's very similar to the AC but with slightly less bottom presence and more mid/high presence. More like the BC, tuning-wise. But better across the board.
I owned the og VC, desert ironwood. I loved it and disliked it (hate to say hated hahaha). On good quality recordings it was amazing. Speed, clarity, dynamics to die for. Just an incredible listen. But...metal....bad quality recordings...headaches and tinnitus! Those metal drives impart a harshness that's not overly problematic unless you have sensitive ears like I do. And with metal they drive me nuts with ringing and fatigue. I have to listen at much lower volume compared to my other sets. So I sold that ironwood. But that was long ago, and my system much improved. Hence I recently picked up another VC, a beautiful stabilized set. And thankfully in my upgraded system they're much easier on my ears. But....still don't like metal/rock on them much. I will listen to it on the VC, but i still lower the volume. And it's not my preferred set for the genre by a mile. Why the long story?
Transition to the CC. I was scared when Zach offered a test unit. I don't like metal drivers, including planars. But no way I'm turning down The Man! He thought I'd like it. I thought Ok, i'll try it, but I know I won't like it. Dam if he wasn't right! I actually love them! I bought that demo unit without hesitation. But lets talk sonics now, as my liking them is out of line with my usual preferences. They're brighter than the VC IMO. There's far more treble energy up top than the VC. So what gives? Somehow, it's smoother and not fatiguing me much at all. And that includes rock/metal. We're talking recorded in a phone booth and the gain turned up to 11, hot and harsh recordings with no bottom end to balance things out. Stuff the VC would shred my ears on. The CC didn't shred my ears. It definitely scared me and made me pucker up! But the anticipated fatigue never came. Huge win for Zach and Dave. To have that much upper mid/treble presence and not be fatiguing is an incredible achievement. And there's a very present bass level to balance things out. It's funny, I ran to my friend who's a huge hifiman guy and tried his collection (while he reveled in mine), and the fatigue was there again. I still hate planars, just not ZMF planars!
Now that we've established the CC isn't fatiguing (to me), lets talk tuning. Compared to the BC/AC, the CC is brighter, thinner, and clearer. It's easily the most resolving headphone in my lineup. It's not thin as a whole, but when swapping back and forth you'll notice it comes across thinner than the others. The bass digs super low and hits hard, but the speed gives it less overall weight, as the decay is very fast. I wouldn't call it analytical as a whole, but compared to the bassy goodness of the others, it's leaning that way. The soundstage is also immense. Less ethereal than the AC, but wider and taller. I do listen to metal on it quite often, but I do sometimes think "I wish I had the BC or AC". I just find them more engaging for those genres. But for blues, jazz, classical, etc they're quickly becoming my go to set.
So how do i personally rank them? AC/BC tie for 1st, CC 2nd, VC 3rd. If you put the Atticus in the mix i'd put it 3rd and move the VC down one. My comments on the AC mostly apply to the AO as well, so just swap AC for AO to get an idea how I feel about them. They're more alike than different, IMO.
Ok to your specific questions (all IMO of course):
And now some questions:
- I know that the Atrium is like a Bokeh on steroids but what about AO vs AC vs Bokeh? How would you rank those three on bass impact, soundstage, detail? - Bass from most to least (overall bass blend, both sub and mid): BC - AC - AO - CC - VC. Soundstage from largest to smallest: AO - AC - CC - VC - BC. Detail from most to least: CC - VC - AO/AC - BC.
- Is the Bokeh just too similar to the AC/AO? Do I need to go with the Caldera to have a collection of complimentary ZMF sound signatures? - Too subjective to really answer. In general if you're looking for variety, i'd go CC. But if you love the BC, the AC is a different flavor of it, and also a blast to listen to. I honestly think if I had to keep two of the three, i'd keep BC and AC and let the CC go. Since metal is my most listened to genre I want the headphones that do it best, and for me that's the BC/AC.
- I've read that the AC is darker sounding than the AO, how are both compared to the Bokeh? Can any of the three be perceived as "fatiguing" in the VC sense ? - In terms of darkness from darkest to brightest: AC - AO - BC. That's with stock pads. Pad swapping can flip that all over the place, so I'll just stick to stock setups. Plus I'm most familiar with the stock pads, I like them best. None will approach the VC's fatigue level. Not even close. Not even the CC, despite having so much treble presence.
- For those of you that listen to rock/metal, which ZMF would your recommendation be for someone who enjoyed such genres much more on the Bokeh than the VC ? - AC all day every day. Try Carach Angren: Franckensteina Strataemontanus for some thunderous double bass blasts. They're epic on both the AC and BC. They make both sets vibrate on my head noticeably. The CC does them well, but the decay is too fast, so though the transient strike is impressive, it decays ultra quick, giving it a leaner overall presentation.
Those are my impressions, based on my preferences. I love warm, moderately fast headphones like the Atticus, BC, AC most. I keep other sets in my lineup for flavor, but gravitate towards those the most.
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