Okay for those who have been wanting a comparison to EFO, I have been doing a bit of A/B testing between E2, EFO, Auteur, Atticus, LCD2, HD800S, Utopia, Aeon Flow Open, HD650 and some Grados.
First of all, i really like the E2's. I started comparing them to all of these others because they have a very unique sound that I really like. They are not just an upgraded version of the EFO; they have a rather different sound signature and frequency response. I realized that I would need to compare them to a wide number of headphones to gauge their competitive advantages.
Before I begin, I'll offer the standard disclaimer that this is just my opinion and warn that I am just writing about my subjective impressions and preferences; I did not go Tyll and measure and compare to Harmon curve or anything. This is just my two cents.
One thing that I noticed while listening to the E2 was that my focus always remained squarely centered around the vocals, which were more forward than the EFO. They were also more lifelike and clear than on the EFO. Listening to the EFO, on the other hand, I found my mind drifting from vocals to various instruments much more freely. This leads me to believe that perhaps the EFO is more neutral as I was reminded of the way that my attention drifts similarly when I listen to HD600 or 650.
So then I brought out my HD650. The signature of the HD650 seemed to have a "family resemblance" to the E2, at least the frequency response, although E2 has much more focus on vocals (and midrange magic?) Quick aside, I've been blown away by my 650s recently and can't believe how good they sound. I think they beat a good number of +$1,000 headphones. The EFO would be more like the 600 with a flatter frequency response.
The E2 has more bass than EFO and it is very high quality bass. Don't expect rumbling boomy bass like a Fostex or something. This is tight and extremely controlled but balanced bass. Plenty of bass for me. Very, very nice.
The detail, accuracy, and 3D imaging of the E2 also reminded me of the HD800S. When I brought those out, I preferred the E2. The E2 is not bright. abrasive, or peaky. I don't know if I'd say it was dark though. It sounds pretty spot on in terms of tone. Like the HD800S it does a great job handling nuanced electronica sounds (thinking of my comparison while listening to Homogenic). Also, like the HD800S they are very light, although they're not as comfortable. The soundstage is huge. Maybe not as big as HD800S with as "accurate" imaging but the best I've heard on any planar and truly top-class.
I compared them to the ZMF Auteur and Atticus too. I have a real weak spot for ZMF and I just love them. Whatever downsides their headphones may have relative to any other headphone, they make up for with their engaging, fun, warm, and natural sounding sonic profile. The E2 and ZMF headphones are really different animals. Quite different, so I can't really give too many insights but I did feel that the Auteur sounded more lifelike than the E2.
To come back full circle, now that I have and love E2, would I sell my EFO? Certainly, not for the time being despite my preference for the E2. The EFO is like a 600 to the HD800S, at some level. I love the EFO because it seems more neutral and all of the frequencies appear balanced so that my mind wanders from one instrument to another with nothing dominating. With the E2, vocals are really out front and center but I like that as well. E2 have more detail, more separation, bigger more accurate soundstage, and a cleaner, more engaging and fun sound but I still love EFO too. They're quite different sounding and I think that the E2 has more of a family resemblance to the Aeon Flow Open than the EFO and also a kind of similar frequency response to the HD650 maybe.
I came up with a tentative relative ranking of my currently owned headphones as a result of this comparison that I'll list for some context.
Favorite non-electrostatic headphones right now
1) ZMF Auteur
2) Mr Speakers Ether 2
3) Focal Utopia
4) ZMF Atticus
5) MrSpeakers Ether Flow Open
6) MrSpeakers Aeon Flow Open
7))HD 800S
8) Grado HP1000
9) Audeze LCD2 with Fazor
10) Grado GS2000E