From personal experience, I can tell you that the UM Miracle is a wonderfully-spacious sounding CIEM
However, what I can also tell you, from personal experience, is that the UM Miracle does not sound right when driven directly by the Cowon J3. The J3 just doesn't control them with enough grunt. Add an amp into that equation and things would probably change dramatically for the better, as the UM Miracle sounds lovely with a HiSoundAudio RoCoo BA or DX100 (DX100 does drive them better than the RoCoo BA, but, for the money, the RoCoo still does a nice job with the Miracles and much better with this particular CIEM than the J3).
So I'm not trying to dissuade you from buying the UM Miracle at all - I'm simply pointing out that it won't make magic if you drive it directly from a J3, so you need to take that into consideration.
If I'm not mistaken, the C4 uses TWFK for tweeter and midrange duties, as does the Miracle, but I'm open to being corrected on that.
Edited by Mython - 12/30/12 at 3:14pm