I took a hard look at the secondary power supply, I have solved one mystery. 

The purpose of the MOSFETs are to split the power supplies for four separate zones. I believe the intent is to multiplex the drivers by rotating the active supplies. 

Power supplies are shared along horizontal rows, in sets of four:

(Colors denote common power supply)

The driver ICs have a max clock of 30MHz. Drivers are arranged into strings of three. With a length of 12b x 16 channels, the length of a string is 576b. This gives a potential max refresh rate (excluding any overhead) of 13kHz.