What qualities stand out in really good solid state preamps?

OP…”That sets a benchmark for those sorts of concerts; but does it do for mixed, PA-driven live music, EDM, etc. what it does for acoustic music concerts?”

Actually, if you think about it, by having a true reference for your system vs the real acoustic world… then you have calibrated your system for all music…and it is going to be correctly interpreting music of any genre.  Then if it was mastered incorrectly… well, it was mastered with a bias. 
 

To get amplified / studio music correct, you would have to reproduce the same electronics / speaker system they were mastered on… and it would only be good for that studio. 
 

@decooney “For a component that is "supposed to be neutral", "adding nothing", looking at history of threads and posts over the past 15-20 years…”

You bring up some good empirical evidence that neutral is not what most people are looking for… although they say they are. 
 

@audiophile1 “I’m trying to refrain from using a term “neutral”. I don’t know if my streamer, DAC, interconnects, cables and components downstream from the source are neutral. There’s just no way for me to possibly know that unless I can A/B what I am hearing at home with what it sounds like in the studio mixed…” 

Good point, but.

There is a way to determine neutral. And it is by becoming intimately familiar with acoustic music in multiple venues. I started my quest a couple decades ago when frustrated that improving one genera would make others sound worse. Over ten years with season tickets to the symphony  (7th row  center) and dozens of acoustical jazz and individual instrument concerts I was quite startled to realize what real music and venues sound like. While there are some characteristics of rock concerts that translates to a system most do not. 
 

When I listen to most systems now they do not sound neutral at all. They are often overly detailed… high lighted details that while interesting makes the venue, miking, mixing, or certain instruments stand out. When cymbals sound like solo instruments, or a triangle grabs your attention then that is not neutral.
 

Bass in natural environments is very nuanced… not slam. My earlier concerns about slam is that the fast slap of bass is not real… in the real world symphonies or rock concerts it is a slower wave with nuanced details. Solid state amps tend to be really good at exceptionally fast rise times and over slap. Now I have realized that even really powerful ones tend to run out of power and therefore do not follow through with the detail.. the articulation of the different frequencies and nuances as the bass arrives. This is something tube amps do well, they reproduce the overall bass experience and nuance well, not pardon the phrase “shooting their load of electrons” on the first wave. Or, at least this is my current theory.

Ok, I could go on and on. But I think neutral is actually the objective of few companies and customers. It is what sounds better to them, which is often hearing things they have not heard before or accentuated instruments or frequencies.   But there are companies and folks that are out to reproduce music as it occurs in the real world.

You ask a good question. I have owned high end amps and preamps since the late 1970’s with Threshold being the first. I finally moved up to tube amps over the last decade.

Different people are looking for different sounds. Some want “high end” sound, which is often exaggerated treble and bass… transparent, highlighted detail, lots of slam and imaging. Lots of older high end solid state equipment has this sound… partially because it was not known how to get good mid-range bloom and great rhythm and pace in solid state into solid state.

This has been improving. Pass recognized this earlier than most with his XA series amps, Now much more natural sounding solid state amps are available from companies like Pass. Going back even ten years though you can loose much of the rhyth and pace.

Getting more natural / musical sound comes first from a good tube preamp… like Audio Research or Conrad Johnson. Then if you are unwilling to go to tubed amps, look at Pass x series or XA series.

There are lots of companies doing the less natural, “high end sounding amps”, like Luxman. There is also MacIntosh, who does powerful heavy midrange / bass amps with under emphasized detai and treble. These “muscle car” like amps are really good at rock music.