Davey, you are asking me to remember what a system from 25 years ago sounded like, but I can try to do it, recognizing that this is filtered not only through my own listening biases but through the rosy glow of memory:
On the old Quad '57' system:
Midrange was just 'there'- natural, unconstrained, human voice was entirely without artifact, except what the recording brought to it, string tone marvelous, horns great within the limits of the system's ability to go loud (some dynamic constriction) and scale- (image size constriction); orchestra worked only in miniature, for both of those reasons, but fine as far as it went. With a sub, there was always discontinuity; I didn't crossover the Quads, I just ran the sub in tandem, because I didn't want the Quads to be filtered through a crossover; the ribbons added air and didn't really bother me as much as the woofer. Adding the rear channels was a hit or miss affair, on some recordings it worked, on others it didn't. When it worked, as the late, great Chuck Lamonica said, when he heard it (a great, characterful, sweet guy who was very much part of the NY audio community who sadly passed away back in around 1991), 'you could kiss every note.'
Compared to what i am running today:
the midrange is just as coherent and unconstrained, at far greater equipment cost, compared to that old system- so that makes the old system crazy good for the money; these days, i have dynamics and an effortlessness with the horns that is much closer to real music on any program material beyond simple human voice and basic instruments (even a small combo, especially horns and drums, can really tax a system); I still have bass integration issues (although better with the latest line stage and phono stage and cabling, but at a cost for those components alone that exceeds by far, the cost of the old system).
The punchline: I could easily live with a Quad 57-based system with the right associated equipment. And whether the current rig I am running is really worth the X factor in cost is probably debatable. I think anybody listening to the two side by side would probably say the current system gets their vote. And, there's probably less 'murk' in the current system, owing to improvements in phono playback and electronics, but even that may be less pronounced than I'm imagining, sitting here thinking about it 25 years later- the Quads weren't a model of efficiency and the noise floor was different than working with 104db horns, so it is essential that I get the 'muck' out of the current system for me to live with it. The Quads probably filtered that stuff, partly through (in)efficiency and restricted bandwidth.
I think that's a fair summary.