Unamped, I find the C3 a little bass light compared to my Clip Zip, no matter which headphones I try it with. It is however, a lovely clean, smooth sound right across the range. Unamped, on balance, I think I prefer the sound from my Zip for the bulk of music I listen to. That statement made though...
Amped, through my Fiio E7 and with either my TF10's or V-Moda M80's the C3 turns into a different animal entirely, it maintains all the clarity and smoothness it has when unamped, but the bass improves. It is a superior sound to the Zip when amped, in every respect. I am not particularly a bass-head, but for some music that I listen to that is bass heavy, I do like that music to come across with the depth, punch and impact that was intended, without sacrificing the mids and trebles, and for me the C3 with the E7 and the headphones I mention, does that exactly. My "goto" album for testing bass clarity and response is 'My Way' by Skazi, ripped as FLAC. It has complex, synthesized bass lines and sub-bass, layered mid and treble synths, and really deep and punchy kick drums. This album is an absolute pleasure to listen to on repeat for a couple of hours when using C3+E7+ M80 or TF10
The C3 is a keeper for me. It's price is right and so is its sound quality. I really like the sound from it when amped, and playing lossless or high bitrate files. It brings both the M80's and TF10's alive and they work really well with it when amped.
I have some GR07's on the way though, I will be interested to hear what it is like with them.