One of the irritating aspects of any DAP player, or as a matter of fact of any headphone amplifiers, is the issue of volume adjustment. When adjusting volume, two common problems occur:
1) left/right imbalance at low volumes.
2) scratching noise when adjusting volume.
One way of eliminating this is to apply electronic adjustment facility (such as the Cowon D2); however, this is usually considered not as handy or comfortable as the conventional analog knob or slide type.
The S:flo2 uses conventional sliding adjustors for the volume which is very comfortable and which I find much easier in adjusting volume level. After more than 10 days of usage, I can safely say that the S:flo2 does not show any of the above two symptoms.
The sound output from the headphone out is very strong. It is definitely much stronger than the output of the Cowon D2 which is rated at 52mW (strongest before the S:flo2 debut).
This is one simply amazing DAP.