From amp designers I know, the XA25 has some of the finesse and sweetness of the First Watt line Pass makes, but no other Pass amp does this (except in the SIT series).
Here’s something relevant:
"Based on actual comparisons, it’s thus fair to say that the XA25 packs virtual Nagra-type small-bottle sonics in the areas of tonal bloom and the ability to track recorded decays. If now we return to Nelson Pass’s 2017 design notes, these results would seem less due to the ‘single-ended’ use of his unusually potent Ixys output devices but what their use eliminated – typical degenerative feedback. It’s how the XA25 differs from our XA-30.8; and apparently how it manages to eclipse it on subjective speed and suchness without sacrificing the usual markers of class A Pass tuning. We’re told that scaling up this recipe to power ratings well beyond the XA25 won’t be easy. In fact, I don’t think it’s happened yet. In that regard, buyers pursuing the smallest amp in the current Pass Labs catalogue actually get something the bigger ones don’t have. It’s bragging rights of a different sort. Here it’s not the guy with the heaviest costliest amp who wins but she who bought smarter speakers which don’t require excess power so can exploit a smaller more sophisticated or purist gain circuit to drive them. In case you’re still reading between the lines: had I discovered the XA25 before I purchased the XA-30.8 as my resident class A example, I’d have saved myself both money and handling fits. I like the sound of the smaller amp even better; and my back much prefers it, too."
https://darko.audio/2023/02/pass-labs-xa25-review/
Also: https://www.stereophile.com/content/pass-laboratories-xa25-power-amplifier-page-2