thanks for the great response!!
michaelplogue, yes, the structural aspect of the render is not quite sound. the model is more or less schematic. i think this is where the overal realism falls short. joints need to show properly, details, materials need better mapping, etc. perhaps a polished render once this is all figured out. i know me and the other big kids would have that thing demolished in a heart beat.
ivox3, the curved studio plane serves two purposes.
1. matte material applied to cast GI shadow (up)
2. shadow material applied to create shadow channel (down)
(and i guess z buff would be in/out)
on the small note, waiting for the new displacement function to be released.
tom, yes matte material + shadow channel = smooth composite.
tyrone, this should answer part of your question. actually the background HDRI i ended up not using. used the original photo instead. masked the render with alpha channel which clipped it nicely into the new image. could have screen mapped the image as alternative.
looking forward to some more composites now that maxwell can easily produce all the needed layers.