Hmm, it looks like we're not mentioning names here, but I've also had a set to test out for a little while now. So here be my thoughts and measurements. (Note: This product is not yet released and could possibly change, though chances of that are slim.)
Subjective Sound Stuff and General Thoughts
I'm not sure what to think of the gold and carbon fiber themed accents, but I certainly don't mind them or the idea. I do think the accents as a whole are a nice touch and honestly wouldn't mind seeing more of them on the headphone to make it all look really consistent. Small thing, though. The visual changes overall are definitely a plus.
In terms of sound quality, I think they sound quite nice. Clean, clear, and articulate. Good sense of air and space. Sound stage is at times a bit too much directly to my left and right sides, but I'm guessing this is at least partially inherent to the base headphone used for this mod/product. Quite smooth, fairly coherent, and laid-back sounding for the most part. Fairly neutral balance with most of the laid-back aspect focused in the upper-mids and treble. They still manage to sound less dull and constricting overall than the PM-1/PM-2 despite still being relatively laid-back.
There are just a couple things I would have to nitpick about when it comes to my silly tastes. First, I think these could use a bit more low-end power (sub-bass). They have good extension and are nicely controlled down low, but I just wish they had more kick and power to them in the end. Not a whole lot more. It just feels a little held back. A touch too thin overall, even from my Sansui 5000A, which tends to give orthos extra thickness and power.
The other thing is there is a very, very slight midrange emphasis to my ears. And while it gives some nice qualities, such as a good sense of harmonics, helps add to lower-end air, and helps give the room a better sense of defined space and resonance, it also has this tendency to, as best as I can put it to words, make everything sound just a touch hollow. I'm not sure how best to describe it, so don't get too hung up on my word choices. I played around with EQ in that area, no more than 1-1.5dB changes, and that seemed to help along with subjectively make the bass come through a bit better.
Lastly, there does seem to be a very slight upper treble emphasis, but not in a particularly offensive area. Plus, it doesn't sound like it jumps out relative to everything else, just in a localized area. It helps with detail.
But, overall, I just have a taste for headphones with a bit more bass and low-mid emphasis (general sense of thickness and power), it would seem. I also don't suspect most others would hear these as slightly mid-centric like I do, but more balanced than anything else. So, keep my personal tastes in mind when taking all of this into consideration. These are quite nice for what they are, and I can certainly recommend them.
I will say that these are a lot better sounding than a stock PM-2 with stock pads. My memory isn't good enough to recall if the stock PM-2 was a bit warmer sounding, but it overall just didn't sound nearly as natural as this headphone. I think I preferred the PM-1's general frequency response a bit more than this mod, but it was just too boring and constricting sounding despite having somewhat thicker low end than the Audio Zenith (again, these thoughts based on potentially faulty memory).
In the end, this is a really nice headphone mod. Clean, clear, fairly natural and open, easy to listen to, and quite balanced or cohesive sounding. There's a lot to like here, and it's something I could easily recommend if you think it sounds like something you'd like. My thoughts overall are quite positive with those nitpicking comments being more a commentary of my tastes.
Measurements
Frequency response looks pretty good. Smooth, laid-back curve. When I was playing around with EQ, I ever-so-slightly toned down the 200Hz-2KHz area, most strongly around 675Hz or so, to make that spot blend in just a bit more with the curve from the bass to treble. That actually seemed to help a surprising amount. The treble peak is not offensive, but a little bit of extra smoothness and perhaps a touch extra treble below that peak area wouldn't hurt either. Sounds nice and balanced either way, just somewhat laid-back. Still, doesn't sound veiled or lacking in articulation.
One thing I've noticed when measuring headphones is that some headphones just have a stronger impact and slightly fuller sound despite measuring close to the same in the bass area (or in general). The Audio Zenith sounds good, but I wouldn't mind a tiny bit more of a boost down low. Personal preference sort of thing.
Ignore those weird bass spikes in the distortion results, along with the slight bass HD elevation that starts in the mids and moves up and you go down the response. Those are just artifacts or limitations with how and what I use to measure headphones. In reality, I suspect this headphone overall has low THD from top to bottom, excluding the inherent midrange HD peak. I still don't think that distortion peak is much of a problem.
CSDs look great, which probably isn't a surprise.
Raw measurements are nicely consistent. Excellent channel matching as well, which I forgot to mention earlier. Very nice matching, really.
PM-1 and PM-2 measurement comparisons in next post.