You can not trust the BIOS readings or any other software for that fact when it comes to voltages.. Those readings have to be wrong. Your PC would not boot at 14v if those voltages were correct. If it did it wouldn't last long.
The best way is to test them with a multimeter.to be sure. There have been plenty of people come through here with abnormal PSU voltages in the BIOS and were completely normal when tested with an accurate meter. More often than not the sensors that read the voltage are not accurate.
This issue could go either way. It may be a PSU or your MB.
I would do a little more digging before you RMA'd anything.
And if the PSU can't handle crossfire, why does it have 4 PCI-E connectors?
The whole system was running fine for 5 months.
There are many different crossfire set-ups and not one of them will require the same amount of voltage or in this case wattage. If your 2 card draw more than what the PSU can handle then you run into issues. This is where you need to pay attention to power demands of your cards
If you run your system through the Corsair PSU configurator they list no less than a 950 watt PSU min and a 1200 w as the best optiion. I'll agrree that is not really needed for what you have. And AMD recommends a 500w PSU just for one card. Sorry i think you are just taxing the PSU and it cant handle two of those cards.*shrugs*