6 case fans and 1 MoBo 4pin

You have a mix there that needs careful attention to detail.

First, the three Corsair HD120 RGB fans each have two separate power and control systems. On each one there is a connection to be made to the special Corsair Fan Hub and its Controller module. The Hub controls the lighting effects on the three fans, and the controller is just the box with the control buttons for the lights. Separately, each fan has a 4-wire cable ending in a 4-pin connector to go to a mobo fan header. The header powers and controls the fan portion of each unit.

Second, you are mixing 3-pin and 4-pin fans in your plan - four 4-pin (only 3 of these are the Corsair HD120 RGB, you say) plus two 3-pin. You cannot provide enough power for all those from one fan header, so a HUB is the only way to go. It will get all power for the fans directly from the PSU, and will control all of its fans according to the PWM signal it gets from your mobo's SYS_FAN header. BUT there are two important notes for this part of the plan to work.

First thing here is: exactly how does your mobo's only SYS_FAN header try to exert control? The pin count on the header will not tell you that. The header MUST be using PWM Mode for control, because the Hub you will need will have to receive a PWM signal from that header. So, POST BACK HERE your mobo's maker and exact model number (and revision, if there is one) so we can check the details in its manual and verify if this can work.

Now, IF that is OK, then you also will need a very particular Hub to be able to work with that mix of fan types. The issue is that any 3-pin fan plugged into a 4-pin header that actually does use PWM Mode for control will always run full speed. Almost all 4-pin fan headers merely relay the PWM signal from the mobo header and thus have this problem - they cannot control the speed of any 3-pin fan. BUT the Phanteks PWM Hub CAN do this job for you. It uses the PWM signal it gets and the power from the PSU to create its own group of six 3-pin fan ports that use the older Voltage Control Mode. That mode is required for 3-pin fans, and it also CAN control the speed of 4-pin fans. So this particular Hub can be used with any mix of 3- and 4-pin fans.

A couple further notes on that Phanteks PWM Hub. Its manual recommends that you connect it to the CPU_FAN header, and then plug your actual CPU cooler into its white Port #1. That way WILL work if your mobo SYS_FAN header does NOT supply a PWM signal. But IF your mobo can do that (we'll know when we see its manual), you can leave the CPU cooler on the CPU fan header and use the Hub with the SYS_FAN header. We'll advise fully when you post back. Last note is that plugging 4-pin fans into the Hub's 3-pin headers might be hard because of spacing. But that Hub comes with two simple Splitters intended for use when you have more than 6 fans. However, using one of those Splitters will allow you to plug two 4-pin fans into its arms (no spacing issues) and connect that pair to one Hub port. That way you will be able to connect your four 4-pin fans to two Hub ports, and two 3-pin fans into two other ports, and all will be speed controlled.