That was a great link to the valve article.
Harmonics are key to understanding why tubes can be more desirable too many.
It's good to have this discussion. Also the ability to control gain more affectively at lower volume levels I think may also be a huge plus. Which I believe explains the Fuller sound at lower volume settings. So it's a combination of harmonics and gain Control that are handled differently by tubes that -yield a desirable outcome.
I need to better understand odd and even harmonics, and how they interplay within a tube amplifier. The article touched on this and was helpful.
I have on order a 300 W tube Mono block amplifier pair. And I've also kept my solid state 600 w mono amplifiers so it will be an interesting comparison.