wut? hifi mags back in the 60s and 70s were very definitely interested in reproducing fine details in audio. or am I misunderstanding you somehow?
The 60s and 70s were different times.
An average consumer in the 60s would not easily get access to the finest recording on the best medium (Reel to reel) So, reaching full potential with hi-fi was not like it is these days. A reviewer might have had a demonstration of some sort. But it was potential that was practically never reached by the largest group of consumers. That also applied more or less in the 70s. But with a key difference.
Producers, labels, R&D of home gear manufacturers were aware of the developments of the CD prototype by the mid 70s (The first prototype was released in the early 80s) So, for the first time apart from some niche disc formats they had sight on a certain new age that the original studio recordings could be almost 1:1 transferred onto something uncompromising and crystal clear for the masses of end users. Which replaced vinyl. The best metaphor I can find is the time that everything "TV" became HD-ready. No HD yet, but... wait for it.
Musicians and producers alike were already working ahead to be CD-ready with a lot of more focus on smoothness of recordings and many remasters of albums were made after because both the CD and the hifi that moved along revealed too much.. In some ways the CD has shaped the music profile of the 80s hit lists along. Kenny G, sterile synthesizers, polished rock. An enormous engineering drive to create demo material for the new medium.
So, in a verifyable way.. there is a different world before the transition of the mid 70s (the seeds to the modern hi-fi world), and the 60s. If you bought an amp in the early 70s there was a lot of content in the pop-world that required cutting of harsh edges of certain Jazz records as they were not "insightful". Just listen to some obscure recording by Gillespie. And material like that was plenty on vinyl. To battle that "in your face" sound, amp voicing gave a form of compression.
Things that got later in the 80s tackled with true compression to get the dynamics right for CD and brighter voiced gear with a lot of treble and bass cranking (not having the "needle-management" dilemma with bass) Different eras, One limited (analog), one kind of unlimited (digital). And we like to all see it through the same glasses we see the world of music nowadays. They are truly different.
Sansui also gradually went from warm to a modern voicing along with that timeline mentioned from early to late 70s. Their early warm voiced amplifiers gradually became less warm in sound and more "CD-Ready" by the time their audio unit (au) 317 entered the market.
Sidenote: even classical music had a certain "brilliance' strive along time. Violins have increased in pitch, beyond a440. flutes along. With Operasingers complaining that it asks more than regular strain on their vocal chords.
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some kind of lost art from when times where better 
