I haven't tried to O/C my cards or adjust the voltages but unless i am getting it wrong you can select which card to adjust, and clicking the displayed lock undoes it.
Click on the number to change cards between 1 or 2 or sync
I am in Crossfire with Matrix HD7970's Plat edt.
Rampage iv Extreme.....3930 i7.....32gb Corsair Vengeance....Thermaltake Water 2.0 Extreme....Matrix HD 7970 x 2 in crossfire....Creative Fatality Champion Soundcard - With front drive bay....Themaltake Toughpower XT Gold 1475 watt power supply.....Samsung SSD 830 512gb...Samsung 1TB HD x 2....Samsung Blu Ray drive....Samsung DVD drive...Windows 7 Ultimate....Thermaltake Overseer RX-1 case