From a review at anythingbutipod.com
"The midrange is very slightly recessed, but still very clear and detailed. The mids are great for voices, male and female alike; they sound very human, not as artificial as with balanced armature drivers. The midrange reminds me more of full-sized Sennheiser or Beyerdynamic headphones than of the usual IEMs, which is a very good thing. All the details are there. Nothing seems to be missing from the main parts of the music. Everything is very dynamic and punchy, both in the micro and macro structures of the audio material.
The treble is slightly rolled off, but doesn't lack any details or clarity either. The Atrios do appear to be "dark" sounding phones compared to some balanced armature IEMs, like the Shures or Etymotics, but that makes them easier to listen to for my ears. I can wear them for hours without getting any listening fatigue, contrary to ultra-bright balanced armature IEMs. They have no sibilance at all; they're really smooth. The Shures and Etymotics do have a bit more precision and clarity in the treble regions, but for me the Atrios sound more natural, relaxed, and enjoyable.
Soundstage is quite good, considering the Atrios are in-ear phones with the drivers sitting very close to the ear drums. It's not a three-dimensional experience as on some large, open headphones, but it leaves most of the in-ear competition far behind. Ultimate Ears Super.Fi, Etymotics, or most others don't have any soundstage at all: all of the sound is inside your head. The Atrios can go quite a bit more to the left and right, front and back of your head. The only other IEM I know with a similar soundstage is the V-Moda Vibe, but this one uses an open design, which is a much easier approach to create a realistic soundstage. "