the whole of the -xx db is just to try and match different sound output levels between disparent speakers. so for example, you have a set of 4ohm M80 on the front, and the 8ohm M3 on the side. the volume output of the fronts would be different than sides so you can adjust the +/- db to get them all to sound the same at the same setting on the volume.

Anthem: AVM60, Fosi DAC-Q5
Axiom: ADA1500, LFR1100 Actiive, QS8, EP500, M3, M3comp, M5