Thanks all,
A couple smaller examples showing the results with the HDR luminosity sphere set to be invisible.
One with dark gray background cube sitting behind the balls. One with no cube but planet atmosphere rendered. The main render used no planet atmosphere or planet surface. They were set not to render in the planet object.
In both examples the HDR driven luminosity of the outer sphere, though not directly visible, still lights up the scene and reflection of that invisible sphere is still rendered because the Visible to Other Rays is checked on and when fully Ray traced reflections are used (as they are on most of the balls) they reveal the image of the outer sphere because of Other Rays.
archonforest - the chrome sphere uses a pure black diffuse color and its reflective shader has reflection set to 1.0. Roughness is 0.01, Ior is 9. Highlight is .5
Nothing special really, I think the complex HDR light reflections and all the surrounding ball objects reflecting back make it look more fancy than it is. The main render did use Ray Detail Multiplier of 0.6 for increased accuracy (and more calculating time) of all reflections.
