All right, I couldn't resist so I went back to the car...
Secret menu still shows Stereo.
And my DSP still shows a high amplitude coming from the HU
I guess the latest FSW_PSW.TRC contains updated values that are NOT read from my car, but that are based on the VO that is read from the car.
It seems obvious of course, otherwise reading each module one by one would take much more time...
So my initial question remains: help please.