derSammler wrote on 2020-03-05, 17:48:
Depends on what you mean by "digital audio". Digital read-out? No, that requires Windows 98 or later and compatible drivers/hardware.
If you're talking about reading digital audio from the disc via the IDE interface (aka, ripping) then no, it doesn't require 98. There are DOS ripping tools. However, at least all those I have used are meant for extracting audio tracks to WAV files, not real-time playback, and obviously don't have anything to do with the way other applications (like games) play CD audio tracks.
The digital audio port on the back of the CD-ROM is active in parallel to the analog port any time the drive is playing audio. Use whichever you'd like. In most cases, your sound card -- if it has a digital input -- will sample-rate convert that 16/44.1 stream to whatever its internal DSP sample rate is, process it through the mixer and, if applicable, effects. The output will appear on whatever analog and digital outputs the card has, but it won't be a pure 1:1 copy of the input stream anymore.
IIRC, the digital port on a CD-ROM is just SPDIF, but you might need an appropriate driver to expose that as coaxial or optical SPDIF. (Driver in this case being of the electronics type -- a buffer amp and transmitter IC, typically. Not a piece of software.)