yustr· Vetustior Humo
If your sound card has a digital output, either optical or co-axial, you'll be able to use your receiver's surround sound decoding (Dolbydigital, DTS which include a special low frequency channel for your sub-woofer) when watching movies or listening to SACD DVD-audio (assuming your DVD player reads those formats). Otherwise, you'll have to use the receiver's DSP circuits to simulate surround.A higher end machine might also include optical digital outputs which could give higher calrity and make use of my system's 24-bit/96Khz capabilities.
About a year ago I loaded all of my CD's onto my computer (over 500) and used that as my source. I've since copied all those files (25G) to my new iPod and use only that. The Cd's are down in the basement and only come out when I get in the car. And even that will end once I get a FM connector for the iPod.
So yes, absolutely you can certainly use your computer as THE SOURCE for your primary stereo system. I've not investigated them recently but my experience with speaker systems made to be used with computers has been less than satisfactory. The sound tends to be thin and tin'y and the bass is boomy and lacks definition. Maybe they've improved them as more and more people do as you're contemplating. :4-dontkno