Short List of Amps I prefer over the Pass Labs XA25 or INT 25

FM Acoustics amps are the only ones that come to mind. Expensive as hell though.

Does anybody on this thread have experience with Spectral?

Very limited. Got to hear it once at Goodwin's High End in Waltham, MA driving Avalon acoustics with mostly or all ceramic drivers (long time ago).

Sharp as hell sounding, razor like transients. Not really compelled to listen to it.  The presentation (amp + speakers) was the most sterile but also compressed. The transients were sharp, but the music didn't seem to open up.

This was a 30 minute listening session decades ago. Please listen for yourself and take the limited experience I had into account.

Audioguy-Re the Sugden idea. I had the Masterclass IA 4 in the system last week as a test thinking it should be pretty good. Oddly it did nothing special for the sound. I was surprised. Just not a great match for some reason.
Cal- Re the First Watt F4s Monoblocks. I wonder if these worked best with your speakers as your speakers are a harder to drive and the F4s have more power than the XA25?

A 20 year old amp that I prefer over all First Watts and XA25 (which is a souped up FW) is the Plinius SA50 Mk3.  

Listen to that Eric dude he knows everything about everything.