Could this be one reason tubes (and perhaps records) sound better?

The Nelson Pass article where he describes his little harmonics generator goes a long way to providing a clue to the clue deprived. I'm glad Nelson is around as sort of an "anti Ted." Also, well said jnorris2005, as I utterly agree.

I think most designers already knows this but has to find a combination from a lot of parameters. For example the designer of many Parasound amps has said that he worked hard to avoid the 7th harmonics since that don't sound good at all but many circuits produce them. Others may focus on other things.

Some like to use negative feedback in amps to make them measure better and others thinks that destroys the sound. The latest Dartzeel amp has configurable negative feedback. If you hover your mouse on their web site title you can see the phrase "In the name of music: listen first, measure later".
https://dartzeel.com/en/

1+++ atdavid and jnorris2005. Now for a little anthropologic physiology.
There is always noise in our natural environment. Those of us that could identify danger through the noise out-survived those that could not and so our hearing has developed certain sensitivities. We are very sencitive to phase and volume for location and we have a canny  ability to evaluate and identify important sounds through noise. The difference between a twig snapping and the rustle of wind through leaves. Higher levels of background noise require us to pay even more attention to identify danger. Background noise causes us to focus on important noise like music. We do this without thinking about it. We listen better with background noise. Some of us actually feel uncomfortable without some background noise. After listening to Tape hiss and vinyl noise for all these years digital sounds unnatural because there is no noise and I do believe many of us prefer vinyl because of the background noise but still find the occasional loud pop disturbing. It makes you snap to attention reflexively. Call it dither or bias or whatever. Noise is definitely an important part of the equation. This would be a great subject for further study if it has not been already. 

One night back when I was still playing CDs about as often as records we got to the end of one side when my wife said she was amazed how quiet it was. The record

I like the fact that every day. Is a learning day. When my girlfriend said lp was quiet and clearer I thought she meant it because her youth had crackle and scratch versions and mine was a new 180g pressing.... I'll have to carry out an experiment with her 

Background noise causes us to focus on important noise like music.

I listen better with my wood stove hissing warmth and also with a malt in hand. First point relevant, second not so....