I think the RCA and BNC thing was a bigger deal 10-20 years ago. My understanding and I have not done the math is the slow edges of SPDIF make impedance matching not as critical. With the interfaces and DACs today most of them should shrug off a lot of jitter. Our speakers are pretty immune unless things get really bad.
Does Dartzeel use 50 ohm for analog too? I just read something about that on 6moons and seems they do. It was supposed to be a technical dissertation. I think someone nose grew a few feet when they wrote it. It started with a flawed premise than used flawed examples to make a case. Not good. Not good at all. We don’t normally send audio 0.5km but 0.1km is not unusual with balanced differential AES. With any single ended, the ground loop from the distance will be too noisy.