First we'll count fan connectors, not fans. That is because the Liquid Freezer II system feeds its two rad fans from a cable from the pump, and ALL of that system gets its power and control solely from ONE connection to the CPU_FAN header. So for the case ventilation fans you have the three pre-mounted in the front (and NOTE that these are 3-pin fan type), plus the three you propose to add.
Now, control of the speed of 3-pin fans is done differently from how it is done for 4-pin fans, and that is selected by how you configure the fan header they plug into. So you MUST arrange your three front 3-pin fans together in one controlled power source, and then the other three in another group with their source suitably configured. I suggest the three additional ones you buy should be the newer 4-pin PWM type, BUT you could buy them ALL as 3-pin type if you wish. This organization means you will need to use two mobo fan headers configured differently, and at least one of them will have to be set to Voltage Control Mode (see later). Thus, each group of fans has three members. The limit of a mobo fan header is max load of 1.0 A, and today's fans all consume from 0.1 to 0.25 A max. So, three such fans connected to one mobo header via a SPLITTER is quite acceptable. Moreover, because those three front fans are 3-pin, you can NOT control their speeds using the new PWM Mode. and that means you can NOT feed them through a HUB. With one unusual exception, all Hubs can control the speed of only 4-pin PWM fans.
A SPLITTER is a simple device that connects all its fans in parallel to the header pins, and all the fan power comes from that header. It has one input "arm" that goes to the header, and two or more output "arms" with male pins to plug in your fans. It has NO other connection "arms". A HUB, on the other hand, has those items PLUS a third "arm" that must plug into a SATA power output from the PSU to get the 12 VDC power supply it sends to all its fans; it does NOT draw power from the mobo header. Here is an example of a 4-pack of Splitters with 2 outputs each.
https://www.amazon.ca/Splitter-Comp...keywords=fan+splitter&qid=1603247282&sr=8-177
Why those? Because I noticed something important on your mobo. First two small points. These are 4-pin fan Splitters, but they work correctly with either 3- or 4-pin fans. Secondly , you take one Splitter and plug it into one output of another. The resulting small "stack" gives you three outputs from one mobo fan header. Since these units have "arms" about 10 " long, this stack places one output about 10" from the mobo header, and the other two nearly 20" from the header. That's the thing I noted. On your mobo, you will use these from the SYS_FAN headers located at the top rear corner, and the middle rear area (see items 4 in the diagram on p. 15 of your manual). So with one such stack you can reach from the top rear corner to the front and plug the top fan into the shorter arm, then run the other two arms down to the remaining front fans. Similarly, from the rear middle header you could reach the rear fan and one of the fans you propose near the PSU at the bottom, and then reach the other bottom fan with a longer arm.
Now on to connection details and header configuration. The Liquid Freezer II system has one 4-pin connector that goes to the CPU_FAN header. I expect that it returns to that header the speed of the PUMP part, and that you will not actually be able to "see" the speed of the rad fans. But that really does not matter. The rad fans are fed from that connection via wires from the pump to the rad slipped into the hose coverings. The CPU_FAN header does all the control of CPU cooling. See p. 33 of your manual for configuration. The details pertain to each fan header, so you must select which header you are changing. For the CPU_FAN header, set Fan Speed Control to Normal, Fan Control Use Temperature Input to CPU (IF there is a choice - on this header you may not have a choice), Fan Control Mode to PWM , Fan Stop to Disabled, and Fan Fail Warning to Enabled.
For the FRONT three pre-installed fans connected to the SYS_FAN1 header at top rear, select that header and set it similarly, with these two important changes: Fan Control Use Temperature Input to Motherboard, not CPU, Fan Control Mode to Voltage (for these 3-pin fans).
For the extra three fans (bottom and rear) connected by a Splitter stack to the rear middle port SYS_FAN2, set it exactly as for SYS_FAN1 with one (possible) change: if you have bought 3-pin fans also for this, leave it the same, but IF you have bought three 4-pin fans for this group, set the Fan Control Mode to PWM.
This connects all your fans to the correct headers with their correct configurations so they all will be automatically controlled by your mobo BIOS according to temperatures measured by the correct sensors. The connections are made using Spltters, not a Hub.When you have made all the adjustments in BIOS Setup, remember to use Esc to return to the Main Menu (p. 25) and choose Save and Exit at upper right to get to the Exit Menu (p. 38). There choose Save and Exit Setup to save all your settings and reboot.
Just a small note about using Splitters or Hubs. Any mobo fan header can deal with a speed signal coming back to it from only ONE fan motor. So any Splitter or Hub that makes multiple connections only sends back the speed of ONE of its fans, and ignores the others completely. This has NO impact on ability to control the speeds. But it does mean that the header cannot do all of its secondary function. It uses the speed signal to detect fan FAILURE, and warns you when that happens. But multiple fans on a single header means it cannot monitor ALL the fans for failure, so you should check from time to time to be sure that all your fans still are working.
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