contact sundown. it's not a bad idea to help pre-amp signal. but if i understand correctly you have a 5v pre-amp? there really isn't a need to go up to 10v. now say if you have maybe a .5v pre-amp signal or a 1.ov pre-amp then there would be a helpfull difference.
Do you notice any hissing or noise (not from a CD or mp3 player)with your current gain setting? If not, then you will not notice any difference at all. If you do, the sound difference will be from the equalizer and not the gain adjustment.