Thanks, Bartosz.
>Would you know how to create and use custom taxonomies for attachments, or how to add custom field values to it?
Sorry, don’t know how to do this. :(
>For now you can use da_get_download_attachments( $post_id, $args ) multiple times and pass ‘include’ => array() parameter with id’s of attachments that belong to specific categories.
I’m sorry, I’ve no idea what this means.