FYI, I sent a question regarding this to asrock last week and still no answer.
Perhaps some of you know:
What amper/watt rating are the various fan headers.
With that info you can easilly determine how many fans you can hook up to a single header.
And since you can only read fan speeds on any 3rd party software for CPU1 & 2 and CHA1 it is most likely best to just hook up other fans directly to your PSU.
My findings regarding to fan speed controll:
1. fan-tastic tuning utility works for CPU1, CPU2 and CHA1 more or less dependably (if it applies those settings on win boot at all). Generally I'd avoid it.
2. If you try to set up a curve for any other fan headers, chances are you'll end up with it being applied to the wrong header and sometimes even stop some fans. Don't bother with it (though it may seem it works at first).
3. CPU1 can normally controll PWM fan through BIOS. Didn't try a 3pin one.
4. CPU2 can controll 3pin fan speed through BIOS but it is same setting as CPU1.
5. CHA1 can only controll 4pin PWM fan. Voltage controll doesn't work if you just plug in a 3pin fan.
So my suggestion for 6 fan setup you have on your radiator would be to get 2 4pin Y-splitters and one 3pin, 4 PWM fans and 2 3pin fans and use the 3 fan headers I mentioned as working (CPU1,2, CHA1). I set up something similar, though for a different purpose (upper intake, CPU push-pull, upper exhaust - I'm an air guy