How to judge a preamp's sound

Thanks for the informed replies. They make sense. (And @russ69 I didn't get the sense they were throwing in amps at random.)

I have read so many posts where people discuss the major differences between amps that I figured it would be hard to estimate the character of the preamp across those differences. I imagined someone trying to describe the flavor of a bland meat in, say, a curry, a tomato sauce, a hollandaise, etc. But this analogy appears to be a bad one. Glad to know better.

@atmasphere Thanks. Those are good suggestions. I imagine keeping the cables the same would be advised in any comparison.

I'm not presently involved in trying out preamps, but I still listen to reviews for fun. I thought I had spotted incorrect advice and was seeking to learn if that was true. 

Hmm. So now we have the claim that:

(a) to hear what a preamp sounds like, try it with many amps and see what qualities persist through the changes.

vs.

(b) to hear what a preamp sounds like, keep the amp the same and then change between preamps to listen for the changes between preamps.

I suppose these are not necessarily at odds, though. They could be complementary?

Another option might also include

(c) Keep the preamp and amp the same, and change the tubes in the preamp only. See what qualities persist through tube changes.

I'd guess that (c) offers the least information, but it would offer some, no?

@teo_audio

Let’s just call it a complex affair that can reach self interpreted conclusions via many different paths.

Everything affects everything so there is no hard set conditionals in any of it.

My limited purpose was to raise for scrutiny a practice -- one metric or method -- which seemed to me to be inherently flawed. I'm no longer sure I was right, given some of the comments above, which are helping me reconsider.

I’m not sure what you mean by "self interpreted conclusions" or "no hard set conditionals."

What seems clear from what people attest to in forums, reviews, and in their living rooms is that some judgments can be made with some level of confidence, despite the multi-variable, relational, and dynamic nature of the phenomena we’re experiencing. Same thing is true with food, wine, relationships...well, everything. We’re in a Heraclitean universe (no stepping into the same river twice) and yet fire burns, sugar is sweet, and metal dome tweeters can be harsh, sometimes.

...and remember, soup isn’t a meal unless there are chunks in it.