I would assume the carefully engineered sound systems in most premium cars are designed to produce the flattest response curves with equalizer settings at center. Thus changing those settings results in tailoring sound to individual preferences rather than producing the most accurate response curves?
I have found that I like the Air's sound best at the preset equalizer settings. My partner is a bass addict, and when he turns the bass up in the Air I find the sound becomes annoyingly bass heavy to my ear. (There is a subtle deep bass line that comes in halfway into Lyle Lovett's "The Road to Ensenada" that I use as a bass reference test. Even at the "0" bass setting in the Air, that bass line vibrates the bottom of the car seats.)