To go along with the whole home theater thing, my wife bought me a Pioneer VSX-D914 digital surround sound receiver. It can handle up to 7.1, but our house is set up for 4.1.
I bought an M-Audio Sonica Theater used off eBay for about $15. Turns out that was a pretty good move. One small caveat, though - you do need to load the software for it or it will work only sort of part-way. Once you load the software, you need to visit its preference program (you can find it in the system preferences, but it actually runs on its own) and set it for the digital output mode. The Sonica Theater actually has a bunch of little 1/8" stereo jacks for 5.1 output, but I bought it to use its coax S/PDIF output.
With the sonica driver and software installed, the EyeTV 500 sent Dolby digital 5.1 audio right into the receiver. CSI:Miami never sounded so good. Although EyeTV has a special setting to get it to send its audio directly to a digital interface, in this instance, you do better to just set the system up to use the Sonica Theater and leave EyeTV alone.
To get the mac DVD player to output correct digital audio from DVDs, I found it was necessary to use its preference to select digital output. Otherwise, you get downmixed stereo.
So now the home theater sounds as good as it looks!