Hey, The Enum option of High and Low or so that of the default Blue and Green works in the connection editor as the following way.
Say I have a sphere and cube, The sphere has an attribute of Hide Cube as an Enum value, what you did was right, going to the connection editor, loading respective attributes in the channels. now you do not get the options of High and Low with the Attribute name. What you need to do is just go ahead by selecting the Enum attribute and the lodvisibility of the object.
You would see that, with Green the object is hidden and when you switch to Blue it will be shown on the screen again.
As for your issue, If you use a 3rd controller to control the visibility of both the elements, you might consider using a set-driven key or two custom-channel attributes to control the visibility of the sphere and the cube.
I hope this suffice your doubt.
