Just thought i'd do a quick follow up on my RE-600 impressions. Have been using them for over a month now, but time and time again, I have been duly impressed by their performance. I feed them either with my iPhone 5 while on the go or the Hifiman HM-901 (balanced amp card) while i'm more stationary.
Theres just something really special about their sound signature, vocals are always so organic sounding, effortless but not "in your face" sounding. Vocals appear laid-back, which gives me the impression that i'm in a concert hall listening to a live performance. As an example, a month ago I went for Ben Howard's live concert, when I got back home, I listened to "Old Pine" through my HM-901, closed my eyes and I swear I was back at the concert hall again. Treble is clear and airy and completely free of sibilance, even on songs which I have heard sibilance from all my other headphones.
Bass is quick, with just enough punch. Bass heads may complain as it doesn't give you that "thud" feeling, but coming from the Etymotics ER-4S, this is plentiful.
Soundstage is truly the star of the show for me with the RE-600, especially when its running in balanced mode, which i'm sure Dr. Fang intended them for. Running them off the HM-901 for the first time, I immediately noticed an "out of head" sound. Often listening to IEMs such as my ER4S and Westone W40, you sort of feel that the sounds are confined in a bubble within your head. But not for the RE-600, it extends beyond your outer ears. My only other headphones which are able to do this are the JH Audio Roxanne's, but they cost nearly 2.5x the RE-600.
If there's anything I can complain about them, there is some slight bass bleed when the song gets crowded, but this occurs rarely.
I would easily recommend this pair of IEMs to anyone. It definitely punches way above its price ($400), at some points even coming dangerously close to my JH Audio Roxanne in terms of performance. IMO, it flat out beats my Westone W40, which costs about $150 more and has 4x BA drivers.