I think the Bass and Treble settings may be the top and bottom settings on the EQ, that is why there is no 20Hhz and 20KHz settings on the Eq. Not sure about this, but it would make sense.

 

As I work in a radio station I know a few things about acoustics. Midrang frequencies if are not lowered will cause distortions and loss of dynamics. You really need a very very good ear to adjust the system in the best way.. as it's fidelity is very good either. To see the real efect that the midrange frequencies have over the whole sound try play with the equaliser from a cheap home stereo.

Anyway.. as we are not bats.. we can live with the Logic7 almost whatever the settings are.

 

Lomag, what Radu explained is exactly right.

The V is the most common setting of an equalizer.

But it really depends on what you want to hear. So I would suggest that you sit in your car and then play with it a little bit. bass left, vocals middle, treble right. Moving the bar up over the default will increase, moving it below will decrease it.
BTW, the L7 is the first and so far only stock audio system where I don't have the basses up all the way - and I love to feel the bass. This system is great!