Solved
Is there a simpler way to compute the gain factor in the SCALE stage of the MDF?
To me, it looks like each gain step shifts by "half" a bit, so we could compute the gain as
floor((DSfilt - DScic)*2);e.g. with RSFLT as target and Sinc5/Dec5 + 14bit ADC1:
floor((22 - 25.6)*2) = -7;