Cooler has two connnectors to go to your motheboard
connector 1: which is 3 pin for pump
and
connector 2: which is 4 pin with PWM for the 3 fans (Themaltake supplies a fan hub)
Which motherboard headers should I plug connectors 1 and 2 into
e.g
1->CPU_OPT, 2->CPU_FAN
or
1->SYS_FAN5_PUMP, 2->CPU_FAN
or something else.
I don not have the GA-Z270 Gaming 7 but the GA-Z170 Gaming 7.
Usually CPU_FAN is PWM and CPU_OPT not.
Radiator fans can be attached to the CPU-FAN to manage speed using PWM signal. The pump can be attached to the CPU_OPT connector and speed, if needed, can be changed by voltage. Pay attention to apply right voltages to the pump to avoid it stops.
Any way you can swap fans and pump. In this case pump will go at maximum speed because PWN signal it is ignored. This is a muche safe option for me.