Set the controls mid-way, adjust each control individually listening to the effect it has on various program material (different discs). Once you have the a general awareness of the effects of controling each band individually, return to mid-way settings and adjust conservatively.
You should also notice that turning down the ranges that are too loud has a similar effect on the over all sound to turning up a desired range although you may need to compensate for a lower overall volume with the main volume control. Try to keep everything as close to mid-way as possible for a smoother transition from one range to the next.
Six bands typically correspond to low-bass, high-bass, low-midrange, high-midrange, lower-high tones and upper-high tones. Basically just more discriminate tone controls.
More bass compensation is typically desirable for lower volumes because the lower tones tend to fade in apparent loudness faster than mid and high tones at lower volume levels.