i'm preparing to flatten/tweak my system soon. i'm wondering if i should be doing it from 0db, or +10db? does having the deck's gain on overdrive introduce any kind of distortion?

also, how does loudness work? isnt it that it boosts bass at low volume? but as you get to higher volumes, it eventually goes to a 0db boost? i ask because if i tweak the gain for my sub so there's no clipping w/ 0db loudness, and i decide to go w/ +14db loudness, will i introduce clipping to my sub at maximum volume (0db or +10db, whichever was suggested above).