What 50wpc or higher amps have a totally different sound from Pass Labs, in a good way?

The Xa 25 is designed differently. Most Pass amps are voiced with 2nd harmonic distortion. Older ones use different transistors as well. So there is that. MACS sound different with lots of power. Lots of fans.

I had Ampzilla and Quattre originals and remember power with good sound but i think similar to Pass.  

@wolfie - how do you think the thresholds differ sonically from the pass gear?

Well, there's a "sound" to Pass. I know, it's what I have. And wouldn't call it dead neutral. There are many ways to retain top sounding SS without it being only Pass.

@redwoodaudio,
Threshold gear tends to be leaner, analytical; reminds me of newer Burmester.  Please note, I have never owned/heard the big threshold monoblocks.   From what I gather,  these are some of the best in the line.

Respectfully, 
Jose

Sugden (tired of saying it lol) class A seems to get it right. They have only been doing it for over 50 years. Loving mine driving my Tannoys....only 30 watts! Sounds like more to me. Seldom raise the volume over 10 AM. They (sugden) were the first @ Solid State Class A amplification. Sounds like tubes without the hassle. My tubes are in my Tavish phono stage. This set up works for me. Best I ever heard or had. Took me a long time to get where I am at, ain’t changing a thing. All I need now is my Linn LP 12.....someday...I highly recommend these Tannoy Eatons...beautiful cabinetry and fantastic sound for the money, just shy of 6K. Not into the monolithic color of the day speaker monstrosities available. They look god awful. I prefer the furniture look. If you need a speaker with 10 tweeters to get the high frequencies right, that to me is a turn off.  To each their own I guess ..happy listening...now back to those LP’s...😁