So we cannot just increase the max gain in auto mode? When use manual pots, the core will be in full manual mode?
Correct - for the analogue BST.
ENOS, ENGN enable the 'external' / manual control of offset and gain.
The links on ENDC and GNDC are Argus functions between real pots and a digital potentiometer IC controlled by the Argus micro (off sheet)
The DC inputs were simply a way to get a gain and offset vlaue of 0 - 255 in the core.
0V (0) is zero gain - grey screen
0V (0) is zero offset (black) and 5V (255) is full offset (white)
[I think - might be the other way round]
The digital BST also had a further multiplier factor you could change with the software