BloodyPenguin posted a review of the Gemini HD on Head-Fi.  These are one of many newer IEMs which are now allowing you to “tune” your IEM sound using swappable filters.  Unlike the Shure 846s where replacing the filters is a little involved, most of the recent swappable filter IEMs are much lower in cost and the filters are easily screwed on and off.  From the reviews I have read most of the IEMs have one filter which works particularly well while the other filters either bloat one range or another or roll off the top end.

Review of the Accutone Gemini HD