Terrible sound quality out of DVD player

Alright I have a problem that has been stumping me for weeks and I turning to smarter individuals them my self in order to solve my dilemma…

I recently purchased a sony DVD player with surround sound speakers from a friend of mine. It is probably a year old and has two speakers plus a sub woofer. He said he dropped around 900.00 dollars for it when it was new (and he is a trust worth guy so I believe him). When watching DVD’s on my TV, the thing preforms as expected…great sound and great bass…could not be happier. However, I am also a big music buff so I have my lap top connected to the DVD player as well in order to listen to mp3’s. Now when I listen to music through my computer, the sound out of the DVD player is terrible. My old surround sound system had a 5 speaker setup plus a sub and worked just fine when I rigged it the same way. I am simply running a audio cable out of the head phone jack on the lap top to one of the audio-in ports on the DVD player. I have played around with the sound settings on both my lap top and the DVD player and can not get the quality of sound to increase at all. The new DVD player has every port imaginable. HDMI, Coaxial, S-video, etc…you name it, you got it as far as that is concerned. Despite the excellent audio I get on DVDs, the fact that my mp3 sound is so terrible is killing me. I know it has something to do with the fact that there are only 2 speakers now but I am not technically savvy enough to figure it out. Can some one shed any light on this problem or direct me to some where I made be able to locate the answer on my own. Any and all advice would be greatly appreciated. Thanks.