Да, насчет HDR-pass ответ нашелся. Все просто (как всегда). Если кому интересно...то вот текст:
This problem appears only with HDR *.map files.
The problem isn't HDRI, it's map files.
use an UNC path for the .map file OR move it locally on every box and use 127.0.0.1/maplocation/picture.map
the above tricks will make it work perfectly either with a single box broadcasting the pic to the network or, in the second case, have every box looking locally for the pic (127.0.0.1 being the IP addy a box uses to adress itself)