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

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.

@atmasphere,  interesting and beautiful theory /hypothesis on harmonic orders. it is not easy to imagine how it works in practice. how different harmonic orders are related in phase/time, why their combination should lead to a soft pleasing sound? how many amps with 0 distortion did you see, what you mean when you refer to an amp without any distortion? and what if the distortion is too small, say .001? would then still a several harmonic order sound with distortion be better, by the way, how many harmonic orders give tube amps (all of them the same number)? 

i was a tube fun for 15 year used only tube amps. once i tried a class ab/a amp i was indeed pleased and even released with a clean clear sound that it produced. if your auditioning experience is based on  a sound with distortion, you are merely in a wrong musical world. it is a personal matter whether you like it or not. in painting, i personally like impressionism the most, because i like to see the world in this alternative way. but ii think sound and music is something different, one naturally prefers a natural uncolored sound that come from musical instruments. if there is a luck of some details and sound is not clean,  you do not really perceive what the artists wished to express. 

 i personally do not like colored sound that produce many expensive and extremely expensive amps (and also speakers). they just to not sound right for me. currently, i am pleased with Cherry Megaschino class D amp which sounds very neutral, detailed and clean, is much smaller and consumes much less energy.