Last night I finally gave up on trying to do it the FOSS way, set up a Samba share on a 6-year-old mid-range PC (8Gb RAM, 3.5GHz processor), and got flawless playback on each of my troublesome media entities with less than ten minutes of effort. On a whim, I also tried setting up Plex (a semi-paid service), and got similarly smooth and flawless service. My idealistic 13-year-old self would be horrified to hear me say "I regret all that time I spent messing around with Linux, when I could have just used a Microsoft product, or a different paid product, that Just Work".
(And yes, I'm kind-of intentionally invoking Cunningham's Law, here, in the hopes that someone can suggest a way of tweaking a RPi4 to be an effective media server - I'd much rather use that than have my PC always-on, but if that's what it takes to get decent playback, I will)