How much does the line driver improve the output of the amplifier?

I am using a HIFONICS line driver that boosts the output to 9volts, I also have HIFONICS amplifiers.

I have not installed the line driver yet, I tested the amps today at the lowest input setting of .2 volts. I wasnt impressed...........

I am hoping that this line driver will make a difference in the amplifier power to my subwoofer, a MOJO 12.