Did the Old Receivers Sound Good?

Great question 

I have a set of the pioneer Z series separates in my main setup. 
Specs aside and ears alone this setup for $2,000 would turn heads 

in todays market. All four pieces have been refurbished. 
 

FWIW...my Sony STR-V6 sounds amazing through a set of Focal Kanta No.2 speakers. 

I used to sell audio in the heyday. The mainstream companies like Marantz, Pioneer and etc., seemed to save their audio goodness for their separates. They all made some halo products that to my ears were noticeably better sounding than their receiver lines. Of note, Sansui, Pioneer and Technics had high-ish end separates that really did rival some of the more esoteric brands and were priced accordingly. I know I didn't mention Marantz. To my ears, they didn't have the detail of the other higher end products, just my take. I had some early NAD which were a revelation for the money, but were unreliable.

I have a vintage family room system consisting of a pioneer sx1250, pioneer pl 630 tt and diapason adamantes as my speakers. It sounds really good. Not as good as my reference system but not nearly as pricey and beautiful to look at with all that aluminum and walnut. For my guests, who can’t tell sound quality, they love it immensely because it reminds them of their youth. They are stunned by the sound quality. I believe the synergy between the adamantes and the 1250 is way better than I expected and it all looks so damn pretty. 

In my experience with the receivers of the 70s many had good amplifiers, but few had preamplifier performance to match.  Integrated amps were no different in this respect.  This applies only to transistor gear.  I recall fronting a Sansui AU 5500 with a Marantz 7 tube preamp, using the amp-in jacks and was impressed that the amp sounded as good as the Crown amp I used then, but with the jumpers in, was lackluster, flat, dull.  The Crown D60 was indistinguishable from the Model 8 tube amp, with a/d/s/ L710s.