Seems like you are very right! Initially I thought the difference between EQ on (flat) versus EQ off is just softer at lower decibel db. But now that you mention it, I tested with a few songs and found that EQ on (flat) sounds smoother/fluid and more musical/sweeter. It also makes the sound on some parts of the mids a little more laid back/distant. EQ off besides being louder overall, actually adds a slight layer of aggressiveness/clarity to the music which causes the musical notes to sound a little more edgy/piercing and rough/coarse. So now I try to compensate for the lower decibel of the EQ on (flat) by increasing the volume by +2.5 on the AK240's volume dial (NOT increase the EQ bar +2.5 db; I think changing the EQ bar may introduce distortion).
Overall EQ on (flat) makes the sound a bit warmer/natural but less forward, whereas the original EQ off makes the sound a bit more sharp/analytical and more forward. The soundstage/depth feels the same. What do you think?