You already said that the mix sounds much better played back in Cubase or Wavelab even on these consumer converters.I concluded these converters must be the culprit
and now I believe maybe it's because of the lack of definition they impart, giving a perception of "lacking fidelity”
because of upper mid harshness. I don’t presume to know and simply ask, on a forum I've always known to be friendly,
"How do most of you deal with this?" If you are reading this, and you are someone who presumes to speak for everyone,
I may not have any use for that kind of response.
So, no I'm not presuming to speak for everyone. I'm just stating the obvious conclusion to be drawn from your own testing.
If the mixed file is OK played in Cubase/Wavelab but not outside of them then converters can not be the problem.