Single ended triode amps have higher THD because they don't resort to negative feedback as a band-aid to fix the inherent nonlinearity of pentodes and transistors. Their distortion is almost entirely low (2nd, 4th) even order distortion, which is much less disturbing to the enjoyment of music than far smaller quantities of higher, (3,5,7 etc) odd order harmonics, which transistor amps produce in more than sufficient quantity to toss the musical baby out with the bath water. Feedback, especially global feedback, obscures and destroys fine detail and thoroughly screws up timing.

As to clipping, transistor amps clip like a ton of bricks - one step over the line, and it's like a waiter dropping a tray stacked high with glassware. Tube amps, and in my experience, SET's in particular, clip much more gently, so an occasional overdoing the volume isn't ghastly. On the other hand, if you're using the right kind of speakers, you won't be clipping the amp in the first place. Kept in the linear part of their response, distortion is extremely low, and fidelity to the musical signal extremely high. That's why you hear/read so often that the most important thing is to get the first watt right. Having a lousy first watt, but hundreds more to back it up is not nearly as satisfying as having a handful of watts, but all of them musically communicative.

As you noted about the Yamaha amp, the best solid state amps do little to offend, but they render the music uninteresting and blah. It's not the amp that has no personality; its personality has stripped the composer and the performers of theirs!

Why do you suppose that every year at CES I find a short tour of the rooms exhibiting solid state gear exhausting, while I linger in (most) of the rooms utilizing tube gear - SET's in particular? It's all of the above combined.

I know this will draw a response of "sure ya like it - ya sells it!", but the fact, as several of you know, is: I got into this nutty business because of what the gear I sell did for my listening enjoyment BEFORE I sold it. I'd be making far more money, but having a lot less fun if I'd stuck to MOR gear and a corporate job.