I'm dying here. I have the Mi Box and the Amazon Fire TV, I signed up for the trial of Youtube TV, since $35 is a lot less than what I am paying for PS Vue. The issue I see is there is no way I have found to sideload the app to allow me to watch on my MiBox. My LG remote is god awful for a user experience.
I have the mobile version installed on the mi box. You can use it with a mouse...it's not ideal but at least it works. I downloaded the apk from apkmirror.
Edit: I have the mobile version of the YouTube tv apk, not the smart YouTube thing linked above. Smart YouTube is for a YouTube app alternative and does not give you access to YouTube tv.
Cast it?
Although the ANDROID TV app should be in the Play Store.
http://www.androidpolice.com/2017/11/02/youtube-tv-app-android-tv-now-live-apk-download/
Mi Box is no longer supported and Google pays no attention to Android TV. Google doesn't support their own platform yet is willing to sell you a service they can't use. Fuck them don't pay for it.
https://smartyoutubetv.github.io/
Try Smart YouTube TV. I use it on my Shield because it auto-refresh rate switches.