The version of granny in the expotron is 2.6, we're now at 2.8.21 for the viewer from the RAD site, DG used granny exporter 2.7.0.29. So really we're going to need a copy of that dll...
Looking at the other comments in that thread I'm less hopeful of getting this to work, especially if you've already tried the exporter from NWN2 and things broke.
There is, however no granny2.dll in the Demigod directory that I can find. This could mean any number of things, but if gr2 is using proprietary compression this doesn't make any sense. Does this mean that gr2 is acting only as a container for the raw max files do you think? Looking at the map gr2 in the viewer it says the source file is a max version 9...if gr2 is only acting as a container then it may be possible to get the max bit out without excessive dissection.
EDIT: nope it looks compressed...checking the total size by adding the vertices+indices+tris is far more than the file size.
but then again that makes no sense either...if it was expecting compressed and you hadn't used their tool surely it would fail completely when you tried to import.