Exporting an IBL PBR Material in 3ds Max is largely the same as before. However there are some maps that need to be filled regardless of if they are used.
A full description of the gTexture slots is also presently missing. The GFX files still refer to the old Specular/Normal/Diffuse map syntax, which may not be a reflection of the true purpose of the texture slot.
Please refer to the dedicated confluence pages for track shaders or car shaders, or the live material editor to view more information about the shaders. However, the easiest way however to setup a material is to copy from the S397 Material Library. This will fill in the default textures for each material with appropriate naming to make the slot use clear. Then you only need to replace textures you wish to use.
Please note: 3ds Max does not support the new BC7 and BC5 export formats, please see DDS Export File Format for more details how to quickly create dummy textures for assignment in Max.