Tweakie Ric says trust your ears but what he really means is trust his ears because only he knows what sounds better and best. All his money making self promoting tweaks that take an amp to an 11 are all done without any basis in objective reality- he preaches "everything makes a difference" yet nothing he does can be measured- just "trust him" and his magic ears that everything he thinks is an improvement will be an improvement to all.
Yes, experiments have been done which show that certain measurements can in fact be indicative of the perception of sound. Certain distortion harmonics are generally preferable over others, for example. The job of an amplifier is to reproduce the input at the output as accurately as possible, only larger. Measurements provide an indication as to whether or not the amp is doing it's job. Some people can tolerate or even prefer certain distortions, others want an amp that delivers the input as accurately as possible. Tastes differ but the only people that claim measurements are meaningless and their golden ear is the only arbiter of truth are usually those trying to sell something, like Tweakie Ric.
