Hello,
The majority of National Instruments MIO E-Series Boards have input gains of 0.5, 1, 2, 5, 10, 20, 50 and 100.
For this particular case, if you have an input signal with a range of 0 to +6V (with ADC range of 0 to +10V), you cannot apply a gain of 2 because the input signal would have a range of 0 to 12V, which exceeds the ADC range. The only gain that you could apply, would be a gain of 1.
Good luck with your application!