Rick has connected his computer to his home theater so he can enjoy iTunes. Scott says the best way would be to stream iTunes over the network. He can then access the files remotely. Depending on the AV receiver, it may be able to handle this. A streaming device like the AppleTV or the Roku Box may be the way to go if he doesn't have a network capable AV receiver.
The chatroom suggests using Plex through the Roku Box and his Mac. A USB DAC may be a good option. He could also use Airplay with an Airport Express. Or he could run digital coax and use that.