First of all, your concern with IBL is misplaced as it were, because IBL as a format is called "angular map" and the environment sphere as a format is called "equirectangular". To make one you have made both because you can convert from one to the other using tools. However, IBL as a source of lighting vs. Env Sphere as a source of lighting, well there is no comparison. Env Sphere wins hands down.

Now that we've got that bit out of the way and you now know to stop asking for IBL, and you want to know how to photograph a room with many photos and then distort and stitch those together into an equirectangular photo, google "how to make equirectangular photo". You will also probably encounter the 3rd format, "cube map", in such explorations. Ignore those as you can't use cube maps directly in poser without additional work.

There are too many options to answer in a forum post. There are literally whole books devoted to this genre of photography.

Some tools that come immediately to mind: photoshop, ptgui, hugin

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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)