I'm not sure but when I did mine with the dd-1+ when I switched over to overlap I was at +2 db to begin with I even watched the multimeter to make sure I was in the right voltage area 2
It's cause your going up past the point of clipping on the gain before you hit read and change track slowly go back down to before clipping then go back up to the point of distortion then hit read and change track
Buy a agm battery and try that and u can always do the big 3 all that stuff is removable and can transfer to other cars 2 agm batteries can be ran parallel together
My subsonic is set at 31 hz my box is tuned to 32 but my amp has a 12 db octave and you can find those tracks for the dd-1 that you can download I have mine downloaded