You should try to use the "Toolset Module Manager" plugin to export your main site's custom post types, taxonomies, custom fields, Views, Content Templates etc..
Then on subsite can use the "Module Manager" plugin again to import the exported file.
Please note that you will able to export/import the structure of post types, taxonomies, custom fields, Views, Content Templates etc.. not the content added to such structures - like posts belongs the post type. It will only help you to export/import structures.