nelson pass' amps can sound rather different from each other, based on version, power level, and topology... can’t lump them all together in my experience - different models give you something but you give up other things
arc ref 75 is definitely a special amp... se running kt150’s are an improvement in some applications, not others, as tube amps and their interface with specific speakers matters much in how the pairing sounds at end of day - once again, depending on the system and taste of the listener, the right pass amp can please as well or better than a ref 75 -- what we are dealing with here are absolutely top notch examples of products of their specific type
(i have both pass xa25/fw f5t as well as ref 75)