me.. really intrested in this topic too.
(Looks like a rabbit hole to me)
First I would add that the overall volume I'm playing, would lead me to 'fine' adjust levels between different rigs.
I mean if I simply go from kpa into PA mixer, I'd change rig's level/volume depending how loud the PA is actually pushing the whole mix (my guitar+everything else)
Second, beside loudness general level, I'm not sure the 'so called' kpa's cab driver is directly involved in what You said.
I mean I usually play My rigs, (Merged profiles tecnically speaking) where kpa has been carefully informed what the DA profile is, and what the cab+mic is. So I woudnt point the cab driver.
I'd say that if I use the kpa with a real cabinet (monitor out, cab off) in a live/rehers situatiuon, the real cab speaker (model and size of course) becomes a crucial part of the sound perceived in the room.
Even in this scenario I'd change something about ( general monitor's EQ and) level of those same rigs mentioned before.
I Notice that if I use a i.e. 4x12 I'd tweak profiles in a different way depending if it loads 12-75 T or V30.
Of course I would also change the level/ balance between, let s say, Cleans and Dirty Rigs.
in the end I GUESS you can not have the Prefect balance in ANY possible scenario.
You must choose what Must be perfect and what you have to acomodate with.