The Center Image parameter determines how much of the center channel sound goes to the center channel speaker and how much goes to the left and right front speakers. It is analogous to the ProLogic II(x) music mode parameter called Center Width.
I don't understand the range 0,0 to 0,1; there must be settings in between there. I would guess that 0 means all the sound goes to the center speaker and 1 means all the sound goes to the front speakers. 1 is what you want if you don't have a center speaker - that would be what is known as a 'phantom' center. There should be intermediate settings so that you can direct just some of the center to the fronts to widen the soundstage.
For example, on my Onkyo the settings are 0 to 5. 3 is the 'normal' default setting. 5 will emphasize the center and 0 will emphasize the front speakers. On 0, t doesn't quite create a true phantom for me but the center is much lower than it is on the default setting.
I tend to use PLII Music for everything and I have its Center Width just slightly higher than the middle so that a slight bit of the center channel goes to the front speakers. That makes the soundstage slightly wider.
