The point I was making about turning the guitar up halfway was that you need to design amplifier gain stages so that there is not so much gain that the amplifie

The point I was making about turning the guitar up halfway was that you need to design amplifier gain stages so that there is not so much gain that the amplifier hits the rails with a reasonable input signal. E.g. If your preamp stage has a voltage gain of 100 and your expected input signal is 1v p-p but you only have +/-20v rails for the power amp stage, you objectively don't have enough headroom.