A point I would add to my previous post: SETs will typically have distortion levels that are vanishingly low when small amounts of power are being delivered, and that increase considerably as their maximum power ratings are approached or exceeded. That kind of variation of distortion as a function of output power can be perceived as an increase in dynamic contrast, which can in turn contribute to an increased perception of "authoritativeness."
Regards,
-- Al
Regards,
-- Al