The quickest way to root any device with an unlocked bootloader is to simply flash the supersu.zip in custom recovery. The Nexus Player does not yet have a custom recovery, and as such developer "Mark Skippen" has decided to create an easy to use self rooting boot image. This image will also automatically install busybox binaries which means once the process is done you will have full admin privileges. Head to the link below for more info and the download link!
via SkipSoft.net