The HAF-X is an enthusiast's case ..... it is expected that "enthusiast" components are going to be put inside. Enthusiast MoBo's generally have much more fan headers.... ROG boards for example from Asus have the CPU fan, PWR Fan, 3 CHA fans and 3 OPT fans. Enthusiast boards like the ROG series also generally have robust fan headers which can handle up to 2 amps on each header. With typical case fans being about 0.33 amps, there's no harm i ganging two of these up on one channel. If ya thinking "well 6 x 0.33 is still less than 2 amps", think again .... have to make some allowance for inrush current on fan startup. I wouldn't do more than 2 fans per header.
You could get a new mobo... but it depends on how much control over the fans you want. I have a HAF-X running 6 case fans via a fan controller (cost about $60AUS) another option if control isn't your concern depending on the peripherals your PSU can handle you can plug several of the fans directly into one of the PSU ports (note that this means they will run at 100% all the time). An AX1200 for example has peripheral cables with 3 molex connectors per lead meaning you could run 3 fans off the single cable (All you fans should have come with molex to 3-pin adaptors).
And finally depending on the power demands of your fans you can splice two (or more) together to run off one fan header as JackNaylorPE stated.
Let me add one of my favorite bits about running two fans in parallel off one mobo connector. Yes, do it! (And the consensus around here seems to be that most common mobos can handle the start-up current for 2 fans per output connector, but maybe not more.) When you connect two fans' motor wires together so they plug into one mobo connector, I recommend you do NOT connect together the two fan motor speed signal wires. On a 3-pin fan, these are the YELLOW wires. By all means connect together the two black (Ground) wires that go to Pin 1 and then two red (+VDC) wires that go to Pin 2. But the Yellow wires take pulse signals (two per motor revolution) from each motor back to the mobo. It you connect both wires together, the mobo gets a mess of two overlapping pulse trains and cannot make sense of them. Connect only ONE yellow wire to Pin 3 of the fan connector; leave the one from the second motor unconnected.
For 4-pin fans the color codes are different. BUT the first three pins are the same, so again it is the wires to Pin 3 that are for speed signals. Pin 4 has the PWM control signal and these two wires from the two motors should be connected together.
Lutfij I don't quite understand your query? For a 3 pin fan the third pin is the tach line, by only using one you are only getting speed feedback from one fan and using linear voltage regulation to set the fan speed, this will be applied to both fans in parallel, meaning that if both fans are identical they will run at the same speed. For 4 pin fans the forth pin is the PWM line, this is preferable for speed control (power efficiency), by splicing both PWM lines together you are ensuring that the same duty cycle it being sent to both fans and as such the fan speed will be the same.
Does that make sense? Basically if both fans are the same they will both run at the same speed for either 3 or 4 pin.