[garww]

For the most part, a computer and sound card are just like a tape deck. I plug it into one of the set tape jacks for in and out.

Seeing as your speakers are self-powered, you don't use the amp to drive them. But the receiver is usually great for headphones.

So, you use whatever out jacks you have on the receiver. There are usually two tape ots at line level. Better receivers ( integrated amp, because you probably wont get much radio) have in and out between the pre-amp and amp sections for more options.

Should you only have one out you can dedicate it to the computer or the speakers - or get some splitter cables.