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

The Yang (opposite) would probably be Chord or Krell.  Switching power supply, error correction, much brighter sound profile.  They are wonderful sounding with the right speakers. 

If you want a higher power alternative to Pass, AVM has a similar sound with its Class AB products.  Decidedly warm and works well with brighter speakers and a ton of power.   

@erik_squires .
I concur. 
In fact, I'd love to compare Pass to Ayre, one day.
Bob

In a good way? Well, that is up to the listener. But if one likes Pass with a particular speaker, it would be difficult to go the opposite way and call it "in a good way" I suspect.

But opposite of Pass? (which I consider just on the warm side of neutral in general). I don’t consider it syrup either though. I consider Moon (more recent stuff) to be just to the brighter side of Neutral but certainly not crazy bright.

Bryston comes to mind, anthem does also, Krell, though they seem to be trying to get away from that.

Agree with erik_squires. I’ve owned both Ayre and Luxman products. Neutral, uncolored, clear, natural sounding. It’s a matter of taste and matching to your other equipment, speakers and room.