only reliable way would be to blind compare

I get why you would think that, but I feel it’s very device dependent. A pre-amp has more going on, therefore more chance to alter the signal (besides what’s intended like volume). But its not a rule.

It’s your brain, not the electronics.

The power amp has the most potential to alter the sound since it is the larger signal

It depends on the kinds of amplifier and to some extent the speaker load.

Non-budget amplifiers designed for high technical performance (e.g. most conventional solid state designs) will these days have no identifiable audible deficiencies with a reasonable speaker load. The low signal level and consequent low power dissipation means the cost of the circuitry required to achieve this for a preamp is small compared to that for a power amplifier. If a power amplifier is required to deliver high current into a low resistance and/or high reactance this requires beefy and expensive circuitry which is why the amplifiers in budget AVRs are poor in this respect.

If the amplifiers are more audiophile where the objective is not a high technical performance but a, hopefully, more attractive sound than the neutral one delivered by a high technical performance amplifier then it will depend on the amplifiers involved. It really isn’t possible to generalise and one would have to consider what each amplifier does to the signal on a case by case basis.

I agree. Especially if your preamp is running some type of room correction algorithms, then it’s definitely doing more to your sound.

I don’t know because I got rid of my analog preamp a long time ago. It’s really unnecessary in an all digital system. Digital volume controls in modern DACs are extremely transparent, assuming the system is gain matched.