Didn't your discrete stereo system have external inputs? I've had an analog cable from my computer's line-out to the stereo system's aux-in from pretty much the same day that my parents let me have my own pc in my bedroom (which was 1996, I think).
These days it's a USB cable rather than a cinch cable, and vorbis/flac rather than mp3, but my PC has been my main music player for more than 25 years -- and the only pair of "game" speakers I've owned were positioned in the living room. Come to think of it, those speakers may very well have been the reason I was allowed a computer in my bedroom :)
Anyway... thank you for prompting that trip down memory lane, I enjoyed it.