I believe you're looking for /r/AndroidTVBoxes/

But be warned that because of the abundance of brands and boxes in this category, there's quite a lot of spam... Best of luck.

Edit: oh and another warning, some of the china boxes come without Google Play/Services, which can be a PITA to install if you don't have a way to root the device. And quite a lot of apps require GSF, so it's not just about using a different app store. Check the apps you need out with Yalp Store before going for a box without Google Play pre-installed.

I cannot recommend any of them. Try an Android subreddit.

This is where you need to be looking for Android OS development.

S912's are faster vs the S905X Mi Box:

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http://freaktab.com/forum/tv-player-support/amlogic-based-tv-players/s912/mecool

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If Xfinity uses DRM for video copy protection - you would have to make doubly sure the DRM capable MECOOL devices actually work with that particular App when using an Android OS.

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