I picked these up from the recent Massdrop, received them yesterday, and was immediately blown away. So of course one of the first things I did was to go see what the Head-Fi discussion was on these and found... not much of anything, which honestly, seems like a small tragedy given the kind of sound quality this IEM produces. While I have a decent amount of experience with relatively high end (eg. LCD-3, HD-800, AH-D7000) full size headphones, I haven't been as fortunate when it comes to IEMs. My highest end IEMs are the Trinity Masters, and I also have some overpriced Beyerdynamics and the great value KZ-ATE's. The S2000 are in completely different league than all of these other IEMs, beating them in every possible dimension. In terms of sound quality, to my ears, they're closer to those aforementioned high end over ears than they are to the Masters (although it should be noted that I don't have the highest opinion of the later). The sound signature has a very mild-V. While I'd prefer a more pronounced mid-range, I'd describe the sound signature as "neutral-ish." Low end is well represented, and definitely the biggest surprise for me. Good extension. Slightly elevated and boomy, which is only really noticeable on tracks that are quite bass heavy to begin with. Otherwise low end feels smooth and quick. High end errs towards clinical. Maybe just a touch sharp with a hint of fatigue, but not noticeably sibilant to my ears. It should be noted that these impressions are "out of the box," so things might smooth out a bit after burn in if you believe in such a thing. Besides being somewhat recessed, mids are well represented. These do a very good job on both male and female vocals, with perhaps a slight edge to the later. Soundstage seems good for IEMs. Decent width, but there's also a noticeable degree of verticality. Detail retrieval is quite good, but suffers moderately when there are a lot of instruments. Other things to note is that these guys are very thin. Not including nozzle, somewhere around 7.5mm at the thickest point and 4mm at the thinnest. The pictures I've seen online didn't prepare me for how small these would be. I'd recommend for Advanced Sound to put up some side profile shots on their store to better convey this. They're easily the most comfortable IEM I've worn. They're also easily the least isolating IEM I've tried. For some people or some situations this might be a good thing, although I assume for most it won't be. The fit is pretty shallow. The nozzles don't have a notch so the tips sit pretty deep on them. I'm fortunate that this suits my ear shape, but I've heard that some people have trouble getting them to fit properly. One user on Massdrop found a solution by cutting a portion of the stem off the small tips which he placed on the nozzles to shorten them. I'm not sure how this might affect things acoustically though. It's possible that my ear shape has something to do with how extremely well I perceive these to perform. But in any case, I hope my impressions are helpful. To me, these IEMs hit so far above their price point that it's almost absurd, and tragic that they haven't received far more attention than they have.