I suggest you look for a headphone (not earphones, it may work better) amplifier, but they're more useful if you use bass supporting headphones. It can balance the treble and bass at the same time without affecting the peak, unlike using the equalizer (mobile, mp3 software), even though it doesn't support this, at least it qualifies it...
(I also had the same problem, I own a Walkman mobile, W715, modified its sound configuration for a superior quality nearer to Audiophile... take a look:
http://www.esato.com/board/viewtopic.php?topic=188767 much better)
The headphone amp. :
http://www.amazon.com/FiiO-E5-Headphone-Amplifier/dp/B001P9EQH8 (I don't think you can find this here)
That's why your option is preferable, i think Cowon mp3 player includes the pre-amp feature. (Also Sony)