I have a QNAP TS-451 with native HDMI output and HD Station which has QNAP player (based on XBMC's last build) and KODI. I use it exclusively in that mode in my media room to drive the projector.
It also runs PLEX server so I can watch my movies anywhere, including iPad, iPhone, Amazon Fire TV, Nvidia Shield.
My movies are in .m4v format as I originally had them on a PC to pull from iTunes to Apple TV but I have abandoned that method now, although I can still do that if I run iTunes on a separate PC.
It also serves as my Slice source and works 100% over Gigabit wired home network. I avoid Wifi unless absolutely necessary (iPad for instance!) I have even disabled Wifi on my Sonos setup and run that hard wired.
In answer to your question about Kodi on Fire TV, it works great but I did have to sideload it and then add a Kodi app that loads it from the home page. Love the Fire TV, also their stick works with Kodi too.
Also all my streaming devices, except Apple TV, work with Anynet+ (Samsung HDMI-CEC implementation).