He does mention the Xonar card as a much cheaper option, but if you're only using the card as digital pass-through, it seems a bit of a waste. Surely, you also need an optical drive with that, too?
The same thread also links to a much cheaper alternative 'recipe' that uses a linear regulated power supply and a much cheaper board/card setup: Building a Media Server as a Digital Audio Transport. That one is really K.I.S.S stuff . . . and about one third the price.