I was just thinking about trying some games from goolge play on my TV through the MiBox and have previously seen the Xiaomi Controller available. I cannot find it anywhere? Does anyone have info about this? Is it possible to use something like my steam controller with the MiBox as a replacement?
Using the Steam controller directly would require root as the only way I've seen to get it out of lizard mode on Android devices is to use one of the standalone Linux drivers within a chroot environment. If you're within mini USB range of a Windows computer you could pick up something like a Titan One and forward the inputs, have the Mi Box recognize it as a 360/One/PS3/PS4 controller, but unless you already have the crossover gaming device it wouldn't be worth it as the price of those is about the same as a new first party controller of one of the main systems. Most Bluetooth controllers should work, especially if they're marketed as Android compatible. I've got an Ipega extending controller that works fine in gamepad mode for instance
You can use xbox360 or xboxone controller, no need for anything more. If you still want xiaomi controller try to find it on aliexpress, gearbest or banggood. For playing games you can also try liquidsky. Good luck