Download latest KitKat stock firmware for M8 TV Box from here or here. Download previous firmware from here.
Model: M8 TV Box
Image file name: ROM_M8-20150120.zip
Image file size: 611 MB
Platform: AMLogic S802
Build number: k200-user 4.4.2 KOT49H 20141009 test-keys
Caution: Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data.