I'm in the same boat. Here are my assumptions.
If you have a receiver with an ethernet port, then you can send the signal direct from the PC to the receiver. Easy enough. I would however need a router so that I can also connect my cable modem to the PC.
If your receiver does not have an ethernet port, you can use a sound card with a digital output. The quality of the sound to the receiver depends on the quality of the sound card. All sound cards are known to make a popping sound and I can't imagine that to be pleasing to hear nor good for the speakers. Basically, it's not a direct route because the data either passes or gets filtered through the sound card. I'm not sure if the data gets passed or filtered, but if it gets filtered, I assume there might be some loss in quality. I'm testing this option right now and the sound is almost as good as a cd/dvd player. I'm trying different sound cards to see if I can get it to sound as good as my dvd player.
I've been told another option would be to get an ethernet to optical cable adapter. I'm not sure if there's a loss in quality, but I can't imagine it would be much. I plan on testing this route too. It's hard to find such an adapter, but I was told the Apple Airport Express does the job. I guess I would also need a wireless router with this route.
