I'm going to change some of the recommendations above based on what you tell us of your hardware.
First, the mobo has two 4-pin headers for CPU cooling - CPU_FAN1 and 2 - that really do use the PWM Mode to control their fans, so those can ONLY be used with 4-pin fans. Then it has three SYS_FAN 4-pin headers, BUT they only use Voltage Control Mode (aka DC Mode). Such a header CAN control the speed of either 3-pin or 4-pin fans. HOWEVER it can NOT be use to connect a 4-pin fan HUB, because that header type does not provide the PWM signal the Hub needs.
Second, the Silverstone Hub is a true 4-pin fan Hub. It can ONLY work when connected to a mobo header that uses PWM Mode, and can control ONLY 4-pin fans. Now, you speak of having "HD 120's" that are 4-pin. The only HD 120 fans I found on the Corsair website are LED units, so maybe that's what you have. But it does not matter if ALL your case fans are 4-pin. You also say that, although the Corsair H70 unit came with a pair of 3-pin fans, you are using a pair of those same 4-pin HD120 models on the H70 radiator.
Under ideal circumstances you would have your CPU cooling system connected to the CPU_FAN header so its automatic cooling controls are based on the temperature sensor inside the CPU chip. Separately, you would have all your case vent fans plugged into mobo SYS_FAN headers and ensure that they are using the motherboard's temperature sensor to guide them. What I will recommend is that you do just that. Even though the three SYS_FAN headers on your mobo use Voltage Control Mode, that method CAN control the speed of 4-pin fans, too. It is not completely ideal, but it works well. The only consideration there, then, is that you have only three such SYS_FAN headers to use. IF you have more than three case vent fans to connect, you might need a SPLITTER (not a Hub) to help out with those.
So, first the CPU cooling system. The H70 system is designed to power and control the CPU pump unit and the two radiator fans separately. For this purpose you can use the Silverstone Hub to advantage. It has two cables that plug in. One ends in a 4-pin female fan connector and MUST plug into a mobo CPU_FAN1 header. (CPU_FAN2 would be just as good for this case.) The other cable must plug into a SATA power output connector directly from the PSU to provide power to the Hub. The 3-pin fan connector on wires coming from the Corsair H70 Unit's PUMP should go to the specially-marked Port #1 of the Hub. This is the only Hub port that can send back to the CPU_FAN header the speed of the device (in this case, the fan) plugged in there. That is important because the CPU_FAN header does extra monitoring of that speed to ensure that it IS working and there is no danger of CPU overheating from poor cooling. Then the two radiator fans can plug into other ports of the Hub. In this configuration, the PUMP will run at full speed all the time because it is a 3-pin device plugged into a 4-pin header using PWM control., and the pump's speed will be reported to the mobo header and closely monitored. Be aware that the BIOS fan control screens may call this speed the "CPU Fan", even though it is really the pump. Then the actual fans on the radiator WILL be speed-controlled by the signals from the mobo header relayed to them via the Hub, based on the temperature actually measured inside the CPU chip, which is ideal. However, there will be NO way for you to "see" the speeds of those two fans - there is no place to send their speed signals for monitoring.
For the case ventilation fans, plug each of them into its own SYS_FAN header. They WILL be speed-controlled automatically by the mobo guided by the mobo temperature sensor, and you will be able to "see" their speeds in BIOS. IF you have more than 3 case vent fans, post back here with a count and we can advise on using splitters if necessary.
See your manual on p.3-30 to configure the fan headers. For the CPU_FAN, ensure that it is set to use the "Smart Fan Mode" for automatic control. For the SYS_FAN headers, ensure that EACH of them is also set this way. But in addition for these three headers, look for an option to specify what temperature sensor is used. If possible, ensure it is the motherboard sensor, not the internal CPU chip sensor, used for these SYS_FAN headers. Remember, when you make any changes to settings in BIOS Setup, you must SAVE and EXIT to save them and reboot.
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