A hybrid approach gives the best of both.

I start with the EnvSphere using the HDRI (as in the last image).

I duplicate my EnvSphere and call it EnvBackground. I move this copy 3 inches closer to the camera (zTran = 3 and my Poser Display Units are inches.) It does not have to be exactly 3 inches. But the point is to make as little as possible of the EnvBackground visible - just enough to see only that sphere in the camera. 

Then on the EnvBackground, I replace the HDRI with the super high resolution LDR (JPG) image.

Now I "see" the LDR, but half of the lighting is coming from the HDR.

We can do a little better.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)