I have a set of Aurisonics AS-2 CIEMs, with the bass porting and with the "awareness" port.
While I think they're wonderful for country, bluegrass, jazz, and some forms of rock, and even favorites for jazz and bluegrass, as the number of instruments and thickness of orchestration grows, there's a point where they go all mushy and indistinct.
It's really quite odd. Mumford and Sons, classical music, almost unlistenable for some reason. Indistinct, headed towards muffled, almost confused sounding. Things like Alison Krauss, ZZ Top, Yes, Rolling Stones, Miles Davis, absolutely lovely, with great imaging, good balance, tremendous clarity.
I'm comparing them to several different IEMs and custom Westone ES-5s (which I can't come up with anything to criticize other than they make poorly engineered music sound poorly engineered...) and to Etymotics of several types mounted in custom ear molds.