No bother chaps.
"electron flow theory in semiconductors. Are electrons flowing or are holes flowing through the conductors?"
Why does it have to be either? Its actually both. Holes are positve and electrons are negative and they're though to 'go round' in opposite directions with an applied potential difference.
These guys are talking about distortion and clipping, btw. There is some truth to the 'presevation of harmonics' while clipping - a transistor just flat lines at its peak voltage, whereas a valve can exceed its rating and retain a nice curvey, but skewed and suppressed wave. In the case that there is clipping, the valve (THERMIONIC VALVE, btfw, not 'tube'; we invented it (I think), we name it, and 'tube' can be bloody anything cylindrical, and anyway, valve is descriptive, thermionic valve doubly so) will retain some form of the information above the rated output where the transistor wont.
Its also true that valves favour even order harmonics, and to most they sound better.
A non-clipping transistor preserves all the information, or near enough, that passes through it.