with the gain know you want to set them in relation to the pre-outs on your head unit and depending on the amp you normally and ohm your running it at will decide what gain you should run at.....gain is just telling the amp what kind of signal is going to receive too much gain(telling the amp is going to get more power then it actually does) is no good same is not enough i would start around .5v-1v....once you set it dont touch it again and control the subs through your head unit