Yeah I did think maybe the phase shifting had something to do with it, still I'm surprised to see such an increase. In terms of frequencies, the most significant thing ARC2 does to my speakers is take out a whole load of boominess. When I flip it on, it certainly doesn't sound like there's an increase in gain. Just the opposite in fact. 

a 5 db increase at 1khz does not sound like a 5 db increase at 80hz....
at a certain volume, and at a certain distance from the speakers, in different rooms....
everything is relative.