Stax SR-007 "Omega II" Open-Back Electrostatic Earspeaker

I'd straight with the bullet point. My review is based on my ears and personal experiences.

GEAR: Fiio K5 Pro -> 100W Class D Speaker Amp -> Stax Srd-7 Pro -> Can

Before EQ
Pros
- The female vocal is Amazing (Coherent and feel 3D)
- Super Details retrieval, speed, transparent
- The best bass for electrostatics (both quantity and quality)
- Very nice bass slam for e-stats
- Superb imaging like a laser

Cons
- Sound muddy due to warm/dark signature
- Stax fart
- Treble roll-off
- Intimate soundstage width

After Oratory1990 Harman Target EQ
Pros
- The detail retrieval shines and clear ( Before EQ, the details are hard to pick out, because of the warm/dark signature. But it's not missing anything)
- Very neutral sound signature
- Even better transparent and soundstage depth (Let's me explain the transparency, For example, where the instrumentals are overlapping each other, and I can clearly hear the separation between each instrument (example vocal and guitar are overlapping the middle, I can hear that the vocal is more forward than a guitar. While another track, a guitar is more forward than the vocal. So this phone can show how it is recorded or engineering.)

- Treble is very neutral, not roll-off, and not harsh.
- Bass and mid are very neutral, not too much or too less
- Still keep the bass slam
- Better soundstage width than before EQ, very neutral, but not as wide as HD800.
- Still keep the speed
- Still keep the imaging

Cons
- Losing the magic of female vocal (Before EQ, it's a bit shouty, but after EQ it's a more neutral sound, the graph also shows 1k shouty)
- Stax fart


Comparison
I currently own all of these three cans. A/B Testing with them directly
KOSS ESP 95X with Stock amp
This can is a mid-centric with mid shouty. I can't listen to it without EQ. After EQ to the Harman target and comparing with O2. It sounds harsher, with fewer details retrieval and speed. Very clearly not transparent as O2. It sounds more coherent and difficult to pick out each instrument. The bass slam is better than O2 but less bass quality (with Harman EQ) But when I boost the O2 bass with EQ, it's clearly better on O2. The only advantage is it is very lightweight(some this is cons), more comfortable than O2, and my ears can breathe better due to the seal.

HIFIMAN Ananda
I really love the Ananda tonality. The treble is one of the best I've heard to date. But after EQ, The O2 is just better over anything, except the Ananda has a taller soundstage which some may prefer. Also since it's planar, the sound has more body. Listening to some music genre (especially hard rock) will be more fun with Ananda.
The soundstage depth(or transparency as I mentioned above (1)) is not that good on Ananda comparing with ESP 95X and O2.

Audio Technica ATH-r70x
The sound has more body. The tonality before EQ is more neutral by my ears. Those are only two advantage, other it's just lose to O2 completely.

Conclusion: If you want the best of O2, Please unlock its potential by doing the EQ and you will be amazed.

If performance is based solely on ultimate transparency, then this is the best headphone I've ever owned and/or listened to. That includes the SR-009. Superb clarity and resolution without any hint of treble brightness or fatigue. Its purity of tone is simply astonishing; it's smooth, organic, airy and fast all at the same time. It adds little to nothing of its own, and neither does it subtract anything from the richness of the music. And for an electrostatic headphone, the bass performance is superb. Tight (!), fast and impactful with plenty of warmth and body. It extends all the way down into the lowest octave, albeit not with quite the same weight and force of an Audeze planar. 

The 007 is built to last, with materials being mostly magnesium and premium supple leather. Solid to the touch and highly comfortable for long listening sessions. 

Very demanding of amplification quality and power, especially in terms of getting the bass right. But rewarding in the end. 

"Farts" when moved/pressed on the head but it's a small price to pay for the sound quality on offer here.
 
I love this freakin' thing. You will NOT be disappointed with this headphone. 

 

This is not really a review, just some inital impresions I'd like to share with fellow head-fiers. I've spent some hours with the SR007 mkI and the SRM007 amp. I also compared the mkI and mkII briefly, and main difference, though subtle, was that the mkII is slightly more forward and bright sounding. I preferred the slightly more smooth mkI. 
 
I've listened to the Stax O2 a couple of times before, but recently I was lucky enough to take it home for trial. When I rigged up the stax rig next to my HD650/Woo WA2, I was eager to see how much more I'd like the Stax rig.... Here's my short comparison
1) o2 is of course substantially more detailed
2) o2 has blacker background
3) o2 has better soundstage, but not by the large margin I'd expect
4) o2 has deeper bass by far and makes music that I really only enjoy on large speakers shine
5) HD650 is way more comfortable. Main issue is velour pads and that the o2 cups don't swivel
6) HD650 is to me less fatiguing. Every time I switched back to the HD650, I felt relief.. The Stax  creates a slight vacuum, and is brighter feeling (though it isn't bright by any high end standard)
7) HD650 has better midrange tonality. The o2 has more detail, of course, but the HD650 has a better flavor. The o2 feels recessed, presenting a "neutral" or "cold" midrange, when the HD650 is warm and natural feeling. 
 
Despite the obvious technical advantages, I preferred the warmness and natural feeling of the HD650, though I really miss the smooth treble detail and powerful bass extension of the O2. 
 
Again please take this "review" with a grain of salt But I wrote it as a reminder that expensive and technically superior isn't necessarily subjectively better - cost no object...