ok here is the content folder:
im sure the cubemap to equirectangular functions could be more elegant 
*i disabled the slight image blurring since it makes the rendering way faster and can be easily done later.
**i added some baked masks to evaluate seams and to test performance vs your mask calculations.
here is an example:
here is an example without seam blurring and without the rear top/bottom eye flip fix:
and here it is with the fix:
now, i have a couple of camera arrangements in mind that may solve some problems (and probably creato others :P)
another way to make this better could be eliminating the seams by UV bending, if this term makes sense.
anyhow, tell me what you think.
thanks again