Can't say I totally agree with some of the above comments, but of course to each their own.
Have owned a DX100 and played with my friends C4, and also currently own a CK4 (modded).
C4 (which is like a ck4 but much better power) is nice, clear and crisp for the upper frequencies. DX100 is more well-rounded (to my ears), but even better soundstage (better front and back vs. C4), resolution and clarity. I feel like the DAC is the difference maker here (and of course it's implementation).
I respectfully disagree with DX100 being an ipod with an average amp (I own an ipc120). If your headphones are good enough, the difference should be really discernible.
I liked C4, but I truly love and miss my DX100 (sold it >.< )
Again, like the above mentioned, go try it and see which flavor you like.