I recently got a mi box (last week) and I have unknown sources allowed from within kodi as well as the system settings on the mi box however i still can not load a repository from the zip file from within kodi. I thought i was going mad but then tried the exact same thing on my pc and it worked perfectly - Is there another setting I am missing ?
It should work, it worked for me.. do you see even the files? Do you get any error message? Have you enabled the debugging and checked the logs?