Not sure if you'd be willing to go this route, because if you don't have the computer with the files in the same room as your stereo, it'll kind of be a pain but...
Apple airport express would be an option to consider. I bought one recently for the purpose of playing my music off my PC through my living room setup. All you need to connect is a wireless network, mini toslink->optical cable ($4), and the airport express itself ($100 or less).
I can stream any music on iTunes through the AX and play it out my speakers in the living room. I can use my wife's laptop, my PC, or a friend's laptop. If it can connect to my wireless network, I can listen to it.
Like I said, the hard part is going to be ease of access if the PC is not in the same room, or you don't have a laptop. I don't mind much because I usually just stream the music when I'm cleaning the house, so I'm moving back and forth from room to room anyway.