Itunes play in high quality 5.1 surround?

So i have a 5.1 surround sound system which can play my itunes from all speakers, but it the sound is really poor quality from the back 2 speakers. I was streaming the radio from my computer, and everything is in a really high quality surround sound system, where the back speakers can be heard perfectly. I was wondering how i could make my itunes play like this. Thanks. I have a Creative Blaster sound card.