What qualities stand out in really good solid state preamps?

@sameyers1 and @decooney 

I had XP-12 for a while before moving up to XP-22. The 12 is a great preamp and gives you a good dose of that natural, warm and extended Pass sound. I had it paired with XA30.8 driving Wilson Sabrina. Upgrading to XP-22 was a good step up though. By no means it’s a night and day difference because the XP-12 is already very good. But there are few major differences mostly due to the separate isolated and beefed up power supply. You get lower noise floor that allows more subtle details to come thru and become more apparent rather than being buried into the mix, better overall clarity, more authority and texture in the bass and bigger, more solid imaging with better instrument separation.
It retains the Pass Labs natural, extended and warm sound signature and the better details it conveys are never in your face. My next upgrade was going from XA30.8 to X260.8. The XP-22 scaled up no issues. 
I’m not a fan of a two box solution but I’m willing to deal with it given the sonic ROI you get. 
 

Here’s XP12 :

and the XP-22 for comparison:

@audphile1 Kudos on your upgrades. I wish they were within my budget.

Do you think the Pass XP-12 is a good fit for the OP, @hilde45 and his Pass Xa-25?

I recommended the XP-12 to @hilde45 in his other discussion. It’s an easy recommendation and synergy with XA25 isn’t even a conversation. But it all depends on the objective and what you’re trying to do. 

@ghdprentice

Good point about calibrating to live music. I suppose that would establish a correlation that could transcend categories. Well put.

Of course, a lot of amplified/studio music should NOT be gotten "correct" because they are compressing and shaping the sound so it pleases and grabs attention when played of mass market headphones, cars, etc. One does NOT want to hear the original. Like a bad casserole, if it’s not corrected somehow, it’s barely edible.
Here’s a pretty tendentious but convincing view on this: https://youtu.be/j_sa915TD-o?si=tOXaeeZvglEhpdAi

The point is that "being in the studio" is kind of meaningless, because they are making stuff to be played by others. The chef cooks food that most customers will like, not what she thinks is "true" or "best."

@sameyers1
Knowing how the XP-12 performs, especially with my XA-25 would be revealing.
I have heard neutrality with a very good passive autoformer. I didn’t like it. Lifelessness -- in that system. Now that I have a DAC with more voltage output, I might try that again. A friend with the Bent/Tap X is done with preamps. he loves it. After 30 years, that’s all he wants in a preamp.

As for "warmer", I can imagine people stuck in a room they cannot measure or tweak with treatments liking a "warmer" sound because it actually helps with some of the tonality deficits produced by their room. Without controls on these comments, there’s no way to really know whether we’re talking about the same perceptual effect. And that’s *prior* to problems we would have with interpretation of these words!

Neutrality is also problematized by our varying physiology.

To comment a bit more -- not about anyone’s comment in particular -- I ask myself, What’s the pragmatic upshot of neutrality? It cannot mean some objective "getting back to the original recording," not least because we'd never be able to confirm we had done so, and most importantly because the original recording is just prime matter which is yet to take on the forms imposed by its varying instantiations (in people's varying gear, ears, rooms, tastes, etc.

Still, we can practically know when something has been added. If I eat a burger covered with black pepper, I would know that’s not neutral. This was ghdprentice's point, I think. One has various baselines and they can notice when there's "something added" vs. "baseline." Objectivity is a pragmatic concept, not a metaphysical one.

@gfguillot
"the more you spend the more you’ll hear in the sound."
Having connected with audiophiles with an eye for small makers and DIY, I’d say the more you KNOW the more you’ll hear in the sound. (And sometimes you know you need to spend more!)

As for "warmer", I can imagine people stuck in a room they cannot measure or tweak with treatments liking a "warmer" sound because it actually helps with some of the tonality deficits produced by their room. Without controls on these comments, there’s no way to really know whether we’re talking about the same perceptual effect. And that’s *prior* to problems we would have with interpretation of these words!
 

Appears as if you have already interpreted and perceived what is meant by these words. 

What do you look for in a preamp @hilde45