> Very, very, few people have their PCs connected to an AV receiver or multichannel speakers
...in part because there's no way to do that, and if you do it by using the headphone jack, in addition to low quality you're also going to get all system sounds
Maybe I am self selecting, but I don't think I have seen a desktop computer or motherboard in the last 15 years without spidf over toslink or RCA. Hell, for that matter a bunch of laptops and even apple until recently included mini toslink/optical out the headphone jack.
I've got an ancient Yamaha 5.1 receiver with no HDMI. I'm sending it audio from a Raspberry Pi4 behind my screen through a cheap USB 7.1 audio card using regular RCA connectors. The extra 2 channels are duplicates of the stereo input (using pulseaudio) and get sent to a stereo amp that goes to 4 ceiling speakers in the adjoining room. I've found that far more reliable than spdif. For example, I can download all of the Dolby test files (including their latest Atmos stuff) and I get 5.1 audio from my old receiver. Using spdif I don't.
I can tell that analog-only motherboard audio is very common even if it doesn't make sense. This was the biggest filter when I was selecting my motherboard, limited the available options just to a handful (within reasonably priced boards, expensive top end of course has all bells and whistles).
...in part because there's no way to do that, and if you do it by using the headphone jack, in addition to low quality you're also going to get all system sounds