IBL's can't 'see' anything specular in P6 or P7, so I'd have to conclude that even using .hdr files with them is going to be limited. IBL's seem to 'blur' any image maps plugged into them to the extreme. Not sure whether they interact with .hdr in the same way. 
Better than nothing I guess, but until specularity is dealt with (most likely increasing render calculations) I can't see Poser's HDRI implementation as much more than a gimmick.

 

PoserPro2014(Sr4), Win7 x64, display units set to inches.

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