there is an alternative option of wiring a JFET so that it takes a feed off Fan A and the 12 V Molex to control Fan B all from the same 3pin fan connector.
Too much bother tbh, I'd have to go out and buy a JFET so I may as well just go and buy some fans that actually work with 3 pin connections XD.
a JFET is like $.50 to $2 depending on where and how robust you feel you need to get.
The point im trying to make is that if I was going to buy a JFET then I might as well buy fans that actually work with the mobo. I'm not trying to wire the fans to save money, it's just that I can't be bothered going to buy some more fans.
From what you posted now I think that as @Dexter_Kane said that the +5V are used to generate +7V. That means, that the fans internally are connected between +5V and +12V which in return results in +7V on the fans motors as +12V - (+5V) = +7V . If they run to loud like that you can try and hook the +12V rail to +5V and the +5V rail to ground as well, this way there should be +5V on the motors of the fans... but its likely they wont spin at all.
Do they spin if you wire it like that:
12V fan A to +5V molex
12V fan B to +5V molex
5V both fans to GND molex
GND both fans to GND molex
I can test this wiring in about an hour, will get back to you once I can.
No luck with the wiring you suggested, I guess I give up then.
Than these fans need the 12 and 5 V to do what ever they internaly do with it.
I think you're going to be better off just replacing the fans with something less weird.
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MAC fans are not the same as stranded PC fans as they get there logic voltage 5 volts in this case from the system board.
Just connect 5 volts to 5 volts. And ground to ground. And then very the 12 volt voltage to change the speed of the fan.
I should also mention that these fan pull a lot of amps so its not a good idea to connect 12 volts to a fan header.