Hi binfordboy, since FBX files contain polygon mesh data and not CAD data, you can write out to an FBX file but not import it in to MoI.

Some more info on that here:
https://moi3d.com/faq#Q:_Why_can_I_export_to_.obj_format.2C_but_cannot_read_.obj_format_into_MoI.3F

The exception to that is if you are doing a sub-d surface conversion. In that case the sub-d importer is on the side pane under SubD > Create > "From file". That can process .obj or .fbx files that contain sub-d control cages.

- Michael