Amazon Fire TV 2 does not support to stream and play MKV files. To address this issue, you can use Pavtube Video Converter Ultimate to convert MKV to Amazon Fire TV readable formats.
Official Guide(More details here): http://www.multipelife.com/stream-mkv-to-amazon-fire-tv-2.html
Pavtube Video Converter Ultimate: http://www.multipelife.com/video-converter-ultimate
Pavtube iMedia Converter for Mac: http://www.multipelife.com/imedia-converter-mac
Still wanna to know more tips about video playback or editing? Please feel free to Email Us: support@pavtube.com