musicgioni, you make good points. I believe that this hobby should be all about enjoyment. So, if you find something that you like and believe that it's better than something else, then for you - it is better. I agree that one cannot take perception out of the equation because perception is how we experience our environment.
In theory, amplifiers could be designed that would have no sonic impact on the signals that they are amplifying. In my experience, though, humans rarely approach theoritical perfection in design. So, again, I agree with you.
I think that the arguments that get made around this forum about amplifiers sounding the same are due in part to (a) the knowledge that some people get fooled by marketing or other factors outside of the sound and pay more for amps than they need to, and (b) a lot of people here haven't auditioned a large number of amps. We can easily perceive that two equal things are different, depending on the context. Check out this
thread from today (especially the link from zhimbo...excellent). So, some people here probably believe that others get fooled by this when it comes to amps. I know that I believe that because I've seen some audio salesman in action. However, without actually hearing your set-up, I think that it would be foolish to claim that there is no sonic difference in your system with different amps hooked up.
People seek measurements as a foundation for an objective means of comparing two or more things to each other. With the enormous number of available amps and the widely varying costs for those amps, that desire makes sense to me. It would be very time consuming and difficult to audition even a fraction of what is available. People want the best that they can afford, so they try to find a way of deciding which component is right for them. To some extent, this can be done. However, with the amount of subjectivity involved in personal preference, it can't get us all of the way there. My approach? Buy something...if I like it, I don't compare it to other things - that way, I stay happy.