FIRSTLY, I want to let you know that I have barely any experience with iems. Beyond that, I'd still like to share that experience, as it is relevant in this case.
So I am using Sony's XBA-3s right now (Triple BA).
It is detailed. It has a clean mid/bass, though I'd say its a little recessed. But my history of iems have been kinda bassy, so what I call recessed, you may call normal. But they're clean.
I can't really comment on the instrument separation. While listening to beethoven's violin concerto in .flac, it seemed pretty good. However, the instrument separation and soundstage was quite a bit better in the soundmagic e30 and pl30 that I have used previously (both are dynamic).
I did have sibilance problems initially, but then I realized that it wasn't due to the iems, it was due to lower quality recordings. Apparently high end iems make bad recordings sound worse. And I did notice that. As I upgraded parts of my library to flac, sibilance problems seem to go away. I just played Karajan's recording of Tchaikovsky's 1812 Overture to make sure what I'm saying is correct, and the Cymbals seem much more forgiving than on any other pair of IEMs I've heard before. If you have any particular song in mind, just tell me to play it through these and I'll tell you what it's like.
However, the XBA's can only be worn straight-down and that's what I dislike about them. I've only found iem's to be comfortable over the ear. Straight down iems also have microphonics problems. To each his own.
There's also the Sony XBA2 (Dual BA), but from what I hear, the XBA3s are considerably better.
What I'm saying is - Don't take my word for it and buy these, I'm not closely experienced enough to give that good judgement. But do include these in the iems you're considering.