The Apple Airport Express has that unique 3.5mm jack that also sends digital optical out. For $99, I think this is one of the easiest solutions. Just plug it in near the A/V Receiver, and run a cable from your airport to the optical input on the receiver. I have this same setup at home and it works great.
I only recently realized the airport has digital output, and have ordered a cable thats on its way from monoprice. This is nice because unlike a DAC or cable, you can have the computer in a remote location and still be able to play music. With a laptop, this might not be as much of a problem, but this lets me enjoy my music from my desktop in the bedroom, on the stereo in the living room.