I am an avid music fan. I listen to a lot of music often with headphones. Early on when I first got an iPod I bought a good pair of headphones. The iPod/IPhone etc sound good but not GREAT. The solution? Add an outboard amplifier and a line out cable. The amplifier is key to drive good headphones so that they develop good bass and create a believable soundstage. I found the amp reviewed below and can say it really makes a big difference. You dont need to spend a lot to get real hifi. But you need to make the effort.
The review link I am posting is about the JDSLabs CMoyBB amp. The CMoy is kind of a public domain design and JDS labs takes it to the max. The article really does a good job of explaining the tech and the sound experiences. Give a read and make the jump.
For the price of a dinner you can get truly great hifi from your music.
Review of the JDS Labs CMoyBB
Here is a compassion of headphone amps including the Cmoy which is the one I bought.
After reading these you will know more then you ever wanted.
But dont waste your money unless you have a good pair of headphones to use with them. A favorite of mine are Grados. Sounds great and not expensive.