No, I don't work for this product but if you want to improve the sound quality of your MP3 players, you must get a quality headphone amp! A good quality one will add more depth of sound.
I just got the PA2V2 headphone amp.
($60) and it's great. You can get it here.
http://www.electric-avenues.com/There's otherones too like the Total Bithead from headroom (headphone.com) which runs about $150. Other products are out there too from various makers.
After listening with a headphone amp, there is no way that I will ever go back to the standard headphone jack directly plugged it.
Also, another way to improve your MP3 player performance is to get better headphones. I use the Sennheiser PX100 (about $40 from Amazon.com) and it's great and considered to be one of the favorite headphones for MP3 players.
Check out
http://head-fi.org/ message board for great tips on audio enhancement with your headphones. Lots of great info. Some of you probably already know about all this that I have mentioned so I apologize if this info is redundant. There might be some newbies lurking and I wanna expose the light of audio enhancement!