Have you tried other input/12ax7 tubes?
I’ve only used 12ax7’s in vintage line and phono stages, as far as HiFi goes, and for added warmth I usually ended up with Amperex or Mullard 12ax7 types over Telefunken.
I much preferred the earlier (17mm plate?) Mullards over the later short plate versions, but this was in vintage gear (might be different with modern gear).
However, Amperex was usually my first choice.
Read about 6h30 vs 6n6p and gather that substitution is a yes/no based upon the circuit bias.
DeKay