Leonard makes a good point, that time to really get comfortable and familiar with the test environment is a good thing. Some of those contrasting impressions I feel could be repeated in the right conditions. Some were still quite fresh and could have evolved over time in their description. For instance, "silky highs" vs. "crisp highs," what does that even mean? If I had another half hour or 45 minutes to really investigate that dimension of a pair of amplifiers, would it did end up a completely different description? Would that contrast have become easier to hear and identify somehow? Might it even have ended up disappearing altogether, something totally imagined? These are all possibilities.
The human imagination is incredibly powerful, I do not understand why it is so difficult for some people to accept that it can affect our hearing, too. I have had it happen to me. I have nothing against faith, nothing against trusting that I can hear something even if it cannot be measured. And I feel no need to prove to someone else something that I know is true and repeatable, especially if it can be replicated from scratch in a different environment. But I am going to need to prove it to myself to be sure I did not make it up. Repeated testing, perhaps over several listening sessions, perhaps over several days, may be needed to get those initial impressions sorted through and settled down to real repeatability and meaningful description.
As a pure guess, I would say that my impressions above are 50% stable and 50% unstable, or in need of more time to mature and even be sure they were real.