It's easy to use Miracast technology to wirelessly mirror your screen to Xiaomi's Mi Box from the Samsung Galaxy S6 family of products like the Galaxy S6 Edge.
On the Mi Box, on the home screen navigate to the far right until you see the green icon for wireless display. Select this icon to start the wireless display connection process.
On the Galaxy S6 Edge, swipe down from the top and select Quick Connect. The Mi Box supports both Miracast based screen mirroring and DLNA based media streaming.
The Quick Connect icons from Samsung don't really make it clear which one is which but select the one which looks like a smartphone held vertically and you will see Start Screen Mirroring. Once you select Start Screen Mirroring, the Miracast connection process will start.
After the connection process is complete, you'll see your Galaxy phone's screen wirelessly mirrored to the TV connected to the Mi Box.
Depending on the wireless quality, with Miracast you may see lag especially on fast action movies but in general Miracast is fine for casual video and photo viewing. If you are having problems, you can also try using DLNA to play media from your Galaxy Phone to the Mi Box.