Case Fans and Splitters

The manual for your mobo says it has only one SYS_FAN header, and it is the 3-pin type operating only in Voltage Control Mode. The "splitter" you linked to actually is a hub adapter device for use ONLY with 4-pin fan systems - mobo headers AND fans. Your mobo cannot supply the required PWM signal to that device so it can work. So no, that is not the solution.

I would suggest a two-part solution since you have three fans now connected directly to a Molex output from the PSU. That connection means all of them are getting a constant 12 VDC supply and running at full speed. BUT this suggestion depends on what type of connectors already are on your three case fans.

IF your fans all have standard 3-pin female fan connectors on the ends of three wires (Black, Red, Yellow) and then you are using some sort of adapter to connect them to the PSU's female 4-pin Molex output, then your task is not too hard. On the other hand, if your fans each have only 2 wires from then ending in a male 4-pin Molex connector with only 2 of its 4 pins in use, then doing what i will suggest would require finding adapters to make it work OR replacing at least two of the fans. So if that latter situation is your case, maybe forget this post.

IF your fans have standard 3-pin female connectors on the ends of their three wires, then you can do this. First you need a 1-to-2 Y-splitter for 3-pin fans like this:

http://www.amazon.com/StarTech-com-12in-Power-Splitter-Cable/dp/B002DY7M1G/ref=sr_1_5?s=pc&ie=UTF8&qid=1461297009&sr=1-5&keywords=3-pin+fan+splitter

It allows you to connect two of your fans to the only SYS_FAN header on your mobo. (You normally can connect 2 fans to such a port, but not more.) That will allow you to use the mobo's normal automatic fan control system to adjust fan speeds according to the actual temperature inside your case, and usually this means running them slower and quieter.

For the third fan it will have to stay connected to your PSU output. HOWEVER, you can buy a set of these "low-noise adapters" for 3-pin fans (you will only need one):

http://www.amazon.com/Noctua-NA-SRC10-Accessory-Low-Noise-Adaptors/dp/B00KG3KELQ/ref=sr_1_1?ie=UTF8&qid=1461296793&sr=8-1&keywords=low-noise+fan+adapter

You inset this into the fan line between the fan's connector and the PSU adapter. It is just a small resistor that reduces fan speed, noise, AND air flow. The effect is fixed as long as you use the adapter - there is no adjustment. As long as that still gives you enough cooling you can leave this fan running slower than it is now.

This two-pronged approach is a way to slow down all three of your case ventilation fans and make them quieter. It depends on the assumption that those three fans now deliver more cooling than you really need and slower fans will still do the job OK. It uses automatic (mobo-based) fan speed control for two fans, and simply fixed reduced speed on the third fan.