[ravenous]

If the question is directed towards me, then it was bagginsbill who gave me that idea.

Yes, it was directed to you - sorry. He was answering your original post, in which you talked about reflecting an image on an IBL light. Firefly reflection doesn't react to lights, and Superfly completely ignores IBL lights.

But after some googling and research I came to the conclusion that there doesn't seem to exist a native Poser object that can function as a skydome/envirosphere.

Not until Poser 11, which does have the 'Construct' object already loaded in the default scene.

But why doesn't reflections simply work with the already existing background?

Because the Poser 'Background' is not an object (with geometry) in the scene. (See bagginsbill's first reply above).

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)