@mahgister, objective proof does not have to have hard numbers, though it can, but critically it must isolate what is being tested, and the test must be repeatable. Saying "I changed this cable and I think it now sounds better", is subjective proof. At a stretch, you may even want to call it evidence. Having someone else change the cable 10 times and not tell you what cable is in the system and you being able to reliably pick the one you claimed "sounded better". That is now objective proof. There is no reducing consciousness to numbers. It is just a matter of reliable identification ... using nothing, absolutely nothing but your ears and brain. The only measurement that may occur is external to ensure levels are matched.
An objective proof in matter of cable is nearly impossible because of all factors implicated and also because it is impossible to reduce experiencing consciousness to numbers dials in principle....And the experiencing of cable difference is most of the time easy to test ourself by replacing one, for sure that is not a proof only an experience.... :)