In many cases a blog platform won’t have an export function, what you’re actually looking for is an import function on the platform of your choice. Wordpress, for example imports from several other platform (Vox is not one of them though as far as I know). If you’re coding-savvy though, you can use this to back it up, and then try to find a platform that can import the file. If you don’t have any luck, looks like you’re stuck with manual methods.