Six items I'll comment on.
1. Any mobo fan header can deal with the speed signal returned to it from only ONE fan. So any fan Splitter or Hub will send back to its host header the speed of the ONLY fan connected to its marked output port (often Port #1) and ignore all the rest. You will never "see" the speeds of those "other" fans on the Hub, but you can assume they are the same if all the fans are the same. This has NO impact on ability to control the fans' speeds. It DOES impact another secondary function of the mobo fan header. It uses the fan speed signal to detect fan FAILURE (zero fan speed signal), but it cannot do that for the fans whose speeds are NOT being sent back from the Hub. So from time to time YOU should check all the fans to be sure they still are working.
2. I believe you already have made this change The AIO system rad fans should be connected to the CPU_FAN header as directed in the instructions for that system. This header always uses the temperature sensor inside the CPU chip to guide it operations. ALL of the fans involved in case ventilation should be controlled from a different mobo fan header, one of the CHA_FAN ones. IF the configuration options for this header give you a choice, make sure to set it to use the temp sensor on the motherboard, not the one inside the CPU chip.
3. As Karadjgne has said above, the six case vent fans control air flow for cooling the mobo and the graphics card, and CPU cooling is done separately. Now the graphics card itself has its own fan cooling system and controls that all by itself - no mobo or case fan direct involvement. But there is a secondary effect from case fans: there needs to be an adequate supply of cool air through the case to ensure that the graphics card's fan system CAN get enough air to cool itself. Usually that is NOT a problem, especially in this case with six fans doing that job. You can examine the graphics card's own cooling system and the GPU temperature using a software utility provided with that card, but NOT via the mobo BIOS. As long as that card is being cooled sufficiently, it is VERY likely that your case vent fans are doing all they need to do.
4. You have no fan mounted at the rear of your case, and it is common to mount one exhaust fan there. On a related note, the arrangement you do have can cause an issue at the top front of the case. The top intake (on the AIO rad) fan is right next to a top front exhaust fan. This results in an air flow "short circuit" so that the air flow in is routed right out of the case and "lost" from a case cooling perspective. I suggest you move the top front exhaust fan to the rear panel as an exhaust. This will ensure better use of air entering through the top intake fan, and better flow of air towards the rear of your case.
5. Personally, I am not a fan of setting fixed fan speeds, or even of doing the two-step fixed "fan curve" you are using. I'm not clear whether you have used that curve on only the rad fans, on only the case fans, or on both. But try out using the mobo's normal default "fan curve" on BOTH the CPU_FAN and CHA_FAN headers. You may well find that you get fully adequate cooling of your entire system for a full range of workloads, but with LESS noise at lower workloads.
6. Recognize the difference between fan PROFILE and fan MODE on a mobo fan header. PROFILE is the method it uses to decide what fan speed to use, and this has options like "Standard", "Manual" (set your own fan curve), "Quiet" (fixed low speed), and "Turbo' (fixed full speed). Separately you can set the MODE, which often has options of "PWM", "DC" or "Voltage", and "Auto". These are HOW the header sends to the fan the signals to achieve the speed that the Profile setting has decided. For using newer 4-pin PMW style fans, set this to PWM; for use with 3-pin fans, set it to DC or Voltage; I recommend not using "Auto" here. Do NOT mix 3-pin and 4-pin fans on the same header.