I have a 2003 dual-processor 2ghz model. The sound chip is a Texas Instruments TAS3004 and the S/PDIF I/O chip is a Crystal Semiconductor CS84xx. Lord knows where you would get drivers.
Can I just add to the chorus here - I absolutely hate it when people ask questions about PowerPC Macintoshes on the PowerPC Macintosh forum. It's a massive breach of etiquette.