http://www.datasheetarchive.com/82C924-datasheet.html
http://www.datasheetarchive.com/CS4231A-datasheet.html
http://www.datasheetcatalog.com/datasheets_pd … MX23C8000.shtml - 1Myte ROM
http://pdf.datasheetcatalog.com/datasheets/120/80203_DS.pdf - 128k ROM
U15 may be a I²S or similar DAC for the proprietary Qdsp sound processor.
The YMF262 and its DAC YAC512 should be well-known.
The smaller ones top right are for analog signals.
LS245 are bus drivers for CDROM.

Thank you very much. It seems like the Opti 924 is the main IC, the "16 Bit Sound Controller."

The Crystal IC is a "Parallel Interface, Multimedia Audio Codec." Not sure if it is optional, but I do have an Opti 931 board with no Crystal chip or equivalent.

Here are snippets from both datasheets. At the risk of sounding dense, can someone help me to understand their functions in layman's terms?

The OPTi card needs a codec to operate. These cards usually use an Analog Devices chip or the pin-compatible Crystal variant.

Thank you. I also discovered that the OPTi 82C931 has an integrated codec, so no need for a Crystal IC. I didn't know that the Analog Devices and Crystal both manufactured codecs. I wonder if a discrete codec means higher quality in general.

Have you seen the ISA sound card overview document in my signature? In addition to cards it lists the common chipsets.

Thanks, gerwin. I did see your excellent resource, but I didn't put two and two together. Very informative and helpful!