*Considering that every single ETA thread for some reason is drawing drama, this will act as the official thread for loaner impressions and conducive discussion. ETA O2 Impressions If you have had the chance to listen to a good unit of the old pre-fazor Audezes and wondered what it would sound like as a dynamic, look no further. The ETA O2 is in many ways a similar headphone: a rather interpretive listen, one that is somewhat unhinged and wholeheartedly unrefined energy (especially in the highs) but not in ways that are necessarily negative. If the Utopia (when driven by synergistic amps) is a posh, stuffy, properly-mannered suited up guy, the O2 is the borderline gangster who wore backwards hats back in the early 2000s and rode a skateboard while carrying around a boombox. There's room for both. Sonics I remember back with the start of ETA, I was having a talk with Evan about bass performance while he was developing the Genesis. Fast forward to the O2, and I have to say that the O2 has absolutely bombastic bass. The O2 has bass you can nearly feel down in your chest (not really, but the closest I've heard from any headphone). I'm not quite sure how it achieves this; it certainly doesn't have the impact and slam of something like the ZMF Atrium, and the pitch differentiation is just a smidge behind the Atrium, but the O2 does deep bass justice. It's what all those dumb-dumb EQ profiles for "bassheads" on the horrible early models of Beats wishes they could do. Compared to the Mini S, the O2's overall sound is more energetic and more "crispy." The transients are noticeably faster and hit a bit harder, but also are a touch more "square" as opposed to "rounded." It's also more resolving than the other Minis but a somewhat noticeable amount, although I still feel that it falls a bit short of the amount of plankton the HD600 can pull. The flip side to this is that with the O2, it's easier to hear the resolution it does pull whereas with the Hd600 you almost have to really listen for it because it's subtle (the HD600 is the a prime example of a headphone with great plankton and very little macrodetail). The weak link in the O2 is the highs. There's no way around it; this is the area where its unrefined energy manifests itself the most. This is more bothersome in some songs moreso than others; although to be fair to ETA, this is a thing with most headphones and their presentations anyhow. In short, it retains some of the sound of the Mini S, has more resolution, is more aggressive, and isn't as smooth in the highs. However the bass performance is utterly bonkers. Amp Pairings In general, I'd recommend something that emphasizes the strengths of the O2. Piety works fine, but I wouldn't use SW51 (the lows on SW51 are not very good and don't complement the O2 well). O2 doesn't need an uber amp to sound great, nor does it need very high power. Build Quality I really do have to bring this up; the area of concern that I had with the O2 is the outer mesh. If you poke at it with your finger, the mesh noticeably bends. However, I have spoken to @tommytakis and I have been reassured that it is quite the durable material; I would ask tour members to please try NOT to test ETA's durability claim but buyers can rest assured. Conclusion If I have to be really honest, I still like the Mini C the best. However the O2 brings some interesting things to the table and I hope to see ETA expand on the ideas used here.