I think measurements can take us to a system that is 90% there. Beyond that, it becomes personal tastes. Some people like a non-flat freq curve, some people like more even order distortion. I think the paramters that govern whether we like or dislike a system are few: mainly frequency curve & distotion, but once the curve is reasonably flat, and the distortion reasonably low (say below 4%) then it becomes subjective.
Just my two cents.
-akhilesh