I made a modification of the player that lifts the sound to TOP portable players. Details here(http://www.head-fi.org/t/564517/colorfly-ck4-first-review/225#post_9762627)
Pros: Sound quality, line out, used material (metal frame), 24bit/192kHz support
Cons: Bugs in the software, only wav supports high resolution, no cue support
The sound quality is very good from the line out.
I think one of the best sounding DAP here, but for sure in the top 5!
The sound is balanced/neutral and detailed, the music background is really black (! later).
I can feel real atmosphere, the instruments are in right positions, not "in the face".
The bass goes to deep enough without any eq, and dynamic too. (with IEM: Audio-Technica ATH-CKM55)
The headphone out can drive low imp headphones, but I can feel the bass rolloff on 56Ohm, and the volume is not enough at all. (with: SUPERLUX HD668B)
I feel sometimes that the sound maybe a bit weak (not energetic).
With Headstage Arrow 12HE (3G) the sound perfect (!)
The real drawbacks:
- some clicking noise during high resolution playback
like static discharge or playback of vinyl rip
nearly every 10 sec is at least one...and it seems on higher resolution worse)
maybe firmware bug?
I translated with google the C4 firmware release log, and found this: "revised WAV format compatibility issues"
- only wav supported for high resolution playback (>48kHz/16bit) ->
hard to fit in the 8GB+uSD (I have 8GB uSD in my phone, but thinking on 16/32GB too)
There is a need for Flac too. -> 32GB uSD is works for me.
- no cover art during playback
- the big screen is without touch technology (i dont care)
- user interface, I mean really simple, and the keys at the top with strange order, but I can still use it, and can learn after a while. At least it is responsive and works fine
- the Line Out can be changed by Volume control
- maybe the battery life only average (but at least >8hours)
- somebody cannot use the EQ funtion
Tested: mp3/flac(44.1/16 48/16 44.1/24 48/24 88.2/24 96/24 192/24)/wav (same)
Not tested: wma/ogg/ape..., video playback (I don't really care about this)
I already tried to contact with the Chinese support for firmware update.
They told they are working on that and expected in 2011 may.