I very much doubt it's 84w per header, that insanely high, fan wattage varies, but is generally around 0.1-0.2a for a 120mm fan, or up to 0.3-0.4a for an led fan.
The PWR_FAN header is normally for a PSU fan connector, some PSU's have a fan connector, it does not power the fan or allow you to control it just allows you to get the fan rpm readings from the psu.
On some motherboards the PWM_FAN header is unpowered but most have them powered but they are not controllable, ie the Q-fan functions will not work on any fan plugged into it.
If it's 24w per header, or 2a, which sounds about right then you might be able to put 6 fans on it, depending on the fan.
Most fans will come with a standard 4pin molex adaptor or connector, which can often be chained together.
How about one of these
http://www.ebuyer.com/138706-nexos-m...case-fans-mfpp (I'm sure scan used to sell them) it lets you run 6 fans off one molex