not all things that matter are amenable to testing.
Indeed we cant test for everything. However we can test for the big three and include that information in our listening. For instance if one amplifier produces a lot more bass from a speaker which amp is right. If the person prefers more bass then he buys that one. However usually when there is more bass the bass is not as good. Its uneven, boomy, the extreme being the "one note" bass. Now if we measure the amp with more bass and find it has poor damping we can say to the first order that is due to the poor damping.
What gets interesting is when we have two very good measuring amps that sound fairly alike and one is tube and one is SS then we have to start wondering as Charlie did, What is it tubes do differently?
I hope someday I make a better amp than what i have made so far. An RM-9 is hard to beat. So are all the Marantz tube amps. Perhaps I have equaled the Marantz 8B, Saul's favorite. Perhaps I have better bass because now we have much larger filter caps than he had. Other than that not much has changed. BTW Saul told me that around the shop they firmly preferred a pair of Mono 8s to the famous Model 9.