I did a very quick comparison of the two (headphone was my CIEMs JH10X3)
The X3 has a warmer and fuller sound, and has a bit more mid-bass.
The Clip Zip is thinner and brighter which makes details more apparent, but the details are also there from the X3.
Soundstaging is similar.
Gapless doesn't work. Upon reading the manual, it seems to me gapless is only supported if there's a cue sheet. I think we need JamesFiio to clarify.
Was there any noise or hiss with the JH10?