Took a quick look into this in PP2010 and I came up with this.  Rendered for shadows only, anything that will cast a shadow, will, including the ground.  When accessing the GROUND in the material room, uncheck *Reflection_lite_Mult.*  This may give problems.  On your directional light, an infinite in this instance, use raytrace and set your *Shadow Blur Radius* to 0.  That will intensify the shadow.  You may want to experiment with AO on the ground material (set up is found in the Wacros) rather than in your light.  I agree with Miss Nancy and millighost, 4 IBL's is overkill.  You misunderstand the concept of Image Based Lighting and how it is applied.  It is an ambient, or global, light filler which is not even necessary in PP2010.  That has been initially replaced by IDL.