I have tested but I did not get it works.
I produced a DEM file with MPC from a shp and bil files (obtained with GlobalMapper from srtm file) and then I made a Join with GmapTool although apparently the Join does work because I could chek resulting img has a DEM subfile, but when I did the Mapsource Project final img did not have DEM subfile (??).
I will try again with other map and more levels. It will follow.

Kind regards