You can use splitters to attach up to 2 fans per fan port header on most mpbos. However, you also need to pay attention to the fan type - specifically, the number of pins it wants to plug into. You mobo has a mix of 2 types. And each type needs a different type of fan AND of splitter.
The main CPU_FAN port is a 4-pin type, so ideally your CPU cooling fan should be the 4-pin type, also called a PWM fan. If you want or need to use 2 fans for CPU cooling, the second fan ought to be of the 4-pin type also and the splitter should be 4-pin design. Now, your mobo also has a second CPU_FAN2 port that is of the 3-pin design. It is not clear to me in the manual why. BUT sometimes this is to give you choices: you can use 4pin fan(s) on the 4-pin port, OR 3-pin fan(s) the the 3-pin port.
The mobo CHA_FAN ports are a tiny bit more confusing. There is ONE 4-pin CHA_FAN1 port where you should be plugging in one (or two, using a splitter) 4-pin (aka PWM) fan(s). There are also TWO other ports, CHA_FAN2 and CHA_FAN3, that are of the 3-pin type, also called Voltage Controlled fans. On each of these you could plug in one (or two using a 3-pin splitter) fan(s) of that 3-pin type.
A 4-pin fan plugged into either port type will work well, it's just that the 4-pin fan design is slightly better in certain situations. A 3-pin fan works properly on a 3-pin port. But on a 4-pin port, a 3-pin fan's speed cannot be controlled - it always runs full speed. That is why you should match fan type with port type.
For splitters, an important point is that both types of fans send a speed pulse signal generated in the fan motor back to the mobo on Pin #3 for monitoring. It is not good to send to a mobo port BOTH pulse signals from two fans on a splitter. So good splitters prevent this, either by not providing a Pin #3 in one of their output connectors, or not providing the wire from that pin. Examples:
3-pin splitter
http://www.newegg.com/Product/Product.aspx?Item=N82E16812423168&cm_re=3-pin_fan_splitter-_-12-423-168-_-Product
4-pin splitter
http://www.newegg.com/Product/Product.aspx?Item=N82E16812423160&cm_re=4-pin_fan_splitter-_-12-423-160-_-Product
There are also devices called Hubs for 4-pin (PWM) fans that allow you to power more than 2 fans from one PWM port. Most ports can't provide that much power (because of heavier momentary start-up currents). But these hubs work by drawing power directly from your PSU with an extra connector, and then sharing the PWM control signal from one port to several fans. However, this can only work in cases of 4-pin (PWM type) fans and ports.
Be aware that using splitters or a hub means that ALL fans connected with such an adapter to the same fan port are being controlled by the particular mobo controller associated with that port. That's not a problem. But it does mean that you should connect to the CPU_FAN port only fans associated with CPU chip cooling; likewise, your chassis ventilation fans all should be connected to the CHA_FAN ports of your mobo.
You can get fans that do not connect to the mobo ports at all - they connect directly to the PSU using a connector called 4-pin Molex originally used as a power supply for HDD's and optical drives. Each such PSU output can power severl fans. BUT there are two significant limits with this fan type:
1. Fans of this type always run at full speed - there is no way for the mobo to change that. The exception is if you also buy and use a Fan Controller which allows you to change the speed of such fans manually, but not automatically via the mobo.
2. Fans connected in this way cannot feed their speed signals back to the mobo for monitoring, so you can't see their speed if you want to.
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