There are several tools that enable you to import ancient models into gmax.
I've used the Universal Model Creator and Converter to extract x files or dxf files from FSDS and FSDS 2 based models.
There are also tools that allow you to create dxf files directly from the FSDS and FSDS 2 models, named mdl2dxf, verious versions available
To convert files like api's etc I've found out two ways: creating scenery files, extract the source code for the file to .sca, adding a new file header so the Trevor Stigter tool MdldisAs and create a new FS 98/FS 2000 mdl. And than converting it with the Universal Model Creator and Converter to get the x or dxf file to import in gmax of max
An easier way to convert api's or disassemble scenery files is to use ModelconvertX by Arnoud ten Haaft, you will be able to extract ready to go 3ds files in a minute. I've converted some CFS 2 and FS2004 Dutch airfield and buildings by Cees Donkers for the Dutch ETO addon this way.
It does not work that well on aircraft models however, but it can deal with library files and it's just a matter of clicking to get several 3DS files. I've converted a lot of CFS 1 libraries this way with much cleaner results than handcoding the .scx files
Converting FS2k4 aircraft can also be done using MDLC to get .sca coded files, which can be imported into gmax with the scam import plugin (and than with Mdlmaker you can get x files. I've converted several CFS 2 ships, tanks etc this way, although the result might get very messy because of the centerpoint of the mdl...
There is an interface with gmax en Deep Exploration, but you must have Max installed to have that working
Guess what I did last night, to be added into the Dutch ETO addon (see attachments)
Deep Exploration has been a great tool, I've been using it for years now to browse and watch any 3d file, from Sketch up to Autocad files
To map simple projects I export an x file, convert it to obj map the obj file with a freeware tool named UvMapper, import back in Deep Exploration, convert to 3ds, import in gmax again, create the LOD if necessary, create the rubble and damage files and than export to m3d files so I can drop bombs on them
See this screenshot for a project I did this way, and also coming in the Dutch ETO Expansion addon (but than with some 100 others)
