CPU_FAN is the primary header and CPU_OPT the secondary. Meaning the CPU_FAN signals to the BIOS that there 'is' an operating fan to cool the CPU and it also signals the 'fan' to increase it's fan speed to offset the CPU Temperatures; i.e. is signals the H100 to increase or lower the fans speed.
Installing the H100 it's best to:
* CPU_FAN - single wire from H100
* 4-Pin Molex (from PSU) to H100 pump; power for both the pump and fans 2 or 4.
* Use the H100's 4-port headers for fans.