Download KitKat stock firmware for CS818II TV Box from here or from here. Download a newer firmware version from here.
Firmware: cs818iisoft0620
Model: CS818II TV Box
Image file size: 258 MB
Image file name: g18ref_yxt9-ota-20140614.V0801.zip
Image file name: g18ref_yxt9-ota-20140614.V0801.zip
Platform: Amlogic AML8726MX
Build number: g18ref_yxt9-user 4.2.2 JDQ39 20140614.V0801 test-keys
Build number: g18ref_yxt9-user 4.2.2 JDQ39 20140614.V0801 test-keys