"It is indeed possible to render depth map shadows when using Diffuse IBL lighting (just like any other light?) if a shadow camera is present for the light." Yep, seems you're right about that, Caulbox. The solution is just to add your own light to the scene, change it to diffuse IBL, then add your IBL image to it in the material room manually. Then you can have shadow maps on that IBL with no AO.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.