Currently showbox for xbox is no available. But you can watch free movies using showbox on xbox by couple with android tablet / smartphones .
You must download and install showbox app for android to your smartphones by follow this post : install showbox on android tablet
- connect tablet to xbox :
1. please uncheck use internal player like images below :
2. select device which connect to your tablet :
3. Done you can watch free movies / tvshow using Showbox on TV through Xbox