My new receiver has a "USB Audio" jack on the front, to which you can hook up a PC and play its audio through the receiver. I thought this was both cool and lame at first - cool because it's such a geeky feature, and lame because I already have my PC sound going to the stereo via normal RCA jacks in the back, so I don't really need it.
But I decided to try it out anyway just to see what it's like... I guess it didn't even occur to me that USB audio would be a digital signal for some reason. That means no hissing during silence when I crank up the volume! That was always an annoying thing about my sound card. I know newer ones are better. Some even have digital outputs.
It's funny - I plugged the cable into the front of my stereo and my PC pops up a window to install drivers for my receiver. :) And yes, the receiver's manual includes instructions and Windows screen shots showing how to set it up. Kinda amusing.
This practically gets rid of the need for a sound card, I think... I'm not sure what kind of volume controls would be available without a normal sound card installed. But anyway, it's just a different playback device. Instead of SoundBlaster Playback or whatever, I select USB Audio from the list. I guess it wouldn't do MIDI files though - no FM synthesis. It will play CDs in the CD-ROM drive digitally though, if the drive supports it. Way cool. Also, my sound card (SB PCI128) doesn't support dual-voice, so for example if I'm playing an mp3, no sound events will be heard. But the USB Audio driver allows multiple simultaneous sounds. Sweet. :)
The receiver's manual says to disconnect the cable whenever USB Audio isn't the currently selected source though. I wonder why. It doesn't explain. Maybe I'll find out soon. Hehe.