Since I have Ph. D. in Biophysics, I do not trust science overall. 😉
There are so many phenomena that can not be explained by science theory.
You had tried Melz 1578 but with some dissappintment.
Tube, cable, tweaks are dependent on system and personal taste or mood.
Now I switch back to Amperex 6sn7 for rounder sound.
But that does not mean that it is the best 6sn7 tube.
I have 70 different kind of 6sn7 or variant tubes to try in my amp.
Thomas