Okay, putting the kinematics definition M669 k1 in front of the driver definition helped in that sense that I can now use 4 out of 8 different direction settings for the four motors (which is in line with my expectation because two motors need to be paired always) instead of only one as was the case before (every other combination resulted in stalling motors).
However, following: https://docs.duet3d.com/en/User_manual/Machine_configuration/Configuration_coreXY#testing-motor-movement again, I can either swap the directions/polarities of both X and Y axis at the same time or I can swap X for Y but I cannot keep X and Y correct and only change the Y polarity as needed, for my Y endstop is at the high end and the tested heightmap (and hence the future print) is mirrored in Y.
Also, its strange that changing the endstop config from high to low does not affect the direction of the homing move as I would expect (but thats maybe due to the formula I copied from the RepRap configurator:
var xTravel = move.axes[0].max - move.axes[0].min + 5 ; calculate how far X can travel plus 5mm
var yTravel = move.axes[1].max - move.axes[1].min + 5 ; calculate how far Y can travel plus 5mm
I also did put the motors at different ports and tried the same thing again but with the same result, as expected.
Out of ideas right now, or is it because of the four wheel drive Iam using (AWD, four motors, Voron or whatever is the correct synonym for it)?