Hi,
your Behringers are no real studio monitors. The MS40 are more of a multimedia speaker set. In another forum i read to reduce the bass to 9 o'clock setting and to push the treble a little to get a better setting.
However, any monitor, no matter how good, is only as good as your experience with them. If you experience a significant change when playing your mix, try to find out what changed and set up your monitors according to it. If your mix has too few bass, reduce the bass setting on your monitors. If the treble is too harsh, increase the treble.
You also have to check your room acoustics - where you put the monitors (not too close to the wall and never inside a corner of the room. Your room has to be treated to prevent too many relfective sound and bass buildups inside of corners. It's not just the monitors. But for the monitors, if you want a good, flat sound, you have to spend at least about 500$ i guess.
Fox