In that case you can try using a rayswitch shader, it can allow your textured sphere to be visible without adding more lighting/reflections/refractions whatever.

- Disable cast and receive shadows on background sphere's shape node
- Make a rayswitch shader and assign it to the background sphere
- Make an mia_mat_x shader and kill the diffuse weight
- Make a mia_light_surface texture and plug into it the mia_mat's additional color
- Plug your background texture into the light surface's color, set the reflection contrib to 1 if you want it to show in reflections.
- Drag and drop the mia_mat_x into the rayswitch's eye slot (if you want your background to show up in reflections as specified in the light surface, drop it into the reflection slot as well, if you want the sky to reflect, just drop the physical sky node in instead. Same goes for refraction)

I'm involving the light surface texture here to simulate a Maya software shader with the image mapped to incandescence(hence killing the diffuse weight on the mia_mat). This has the added control over they sky brightness provided by the light surface's intensity. Plus native Maya shaders cause issues with the rayswitch. Hope that helps.