I just came across your thread and thought I'd tell you what I just did.
I found a product called Pro Hifi Link which hooks up to your computer via USB
and sends data to the reciever via stereo input, digital 5.1, or digital optical.
I can't speak for the sound conversion software/hardware included, but
at under $100, it's worth looking into.

I've hooked it up via stereo inputs and sound is quite good.
Good luck.