Hum.. well first of all your SPDIF is an out that you can hook directly up to your home entertainment system. It's just like the audio out that you would probably have on the back of say your stand alone DVD player. Some have Coax and some have SPDIF. It's a fully digital out instead of having all the multitude of analog cables out. So you could plug your computer audio out to your stereo like I do and then when i play a DVD movie on my computer's DVD player I get full Dolby digital 5.1 on my home speakers if the movie supports it of course.
I am not sure but maybe there are high end computer speakers that also take in the digital out from your computer's SPDIF. My motherboard actually has both the SPDIF and a coax which is nice.
Now if you don't want to use the digital out or you have nothing to connect it to (home theater receiver) then you can get a normal set of computer speakers. Some of the nicer motherboards have 7.1 out. Thus you could get any of the many computer speakers from Creative etc... that have distinct in for different channels (like front, center, rear and sub woofer). Thus on the back of your panel you will probably have a distinct out for center, sub, rear and front speakers and also a Microphone out. You of course don't have to use it liek this. My mobo allows me in its settings to simply set my output to 2 speakers, or a headphone etc and in that case ONE of those outputs gets used a simple LINE OUT which works well enough.