I'm thinking of getting a 5.1 speaker system for my computer but I'm not sure what I would need for it to work. I currently have a SB Live MP3+ card (not the 5.1 version I don't think). I went to Amazon to see if they have any just as a starter and they had one from Creative but it says your sound card needs to be a "4-channel PCI sound card." What the heck do they mean by that?