u mute evrything except ur mids.then try to set it lower slowly.use ur ears to listen whether it can produce the lower freq.if not, then no point setting it too low and ur mids cant produce the sound.in the end, u might have a gap where theres no sound produced on tat freq.normally cross at about 50hz.so u can bring the sub on the front.this is just a generalization.u need to find it urself to suit ur own taste.