Speaking to the processing needed just to pass the PCM data around being a massive fraction of the overall processing power, you'll notice in a lot of early CD-

Speaking to the processing needed just to pass the PCM data around being a massive fraction of the overall processing power, you'll notice in a lot of early CD-ROM games they just completely sidestep this and just use the CD drive to read actual CD audio off the disk and have it decode and play back the audio directly to the sound output device instead of going through the CPU. Essentially the computer would just tell the CD drive "play track 11" when you got to the 11th level of the game. And that was a decade past the creation of the audio CD that normal PCs (or gaming PCs!) still needed a lot of processing power just handling that data stream.