I think you'll be fine setting your gain to 2v on your amp matching your HU voltage to the input voltage on your amp... setting it to 1v will not damage anything, setting the gain above 2v will introduce distortion into the amp... when it comes to a sub amp i usually match my HU voltage to the amp... and for my incar speakers I usually set the gain lower as high frequencies dont require much power to be too much for the ears..