You are right. Everything has been shown and said already. People are smart to realize and decide by themselves what they want to do.Now YOU are the one relying on test tones! Sure, if you want to maximize SINAD or any other spec at one specific wattage, you can vary the input level until you get the amplifier operating at its sweet spot for that measurement. But as soon as you play music that all goes out the window. However, you can continue to write whatever you want. I'm done on this topic. I still maintain that using a preamp for any reason other than having a very low level analog source will measurably and perhaps audibly degrade the sound in most cases, especially if it uses tubes. Anyone who understands math and basic electronics can read the conversation and decide for themselves what they want to do. Enjoy the music.
I'll keep enjoying my setup and my music in the meantime.