Download Android KitKat 4.4.4 stock firmware for MX9 TV Box from here or from here. Download a newer firmware from here.
Model： MX9 TV Box
Image file size: 527 MB
Platform: Rockchip RK31229 / RK322A
Model number: MXR
Boot version: 2.30
FW version: 4.4.04
Build number: rk322x-eng 4.4.4 KTU84Q eng.foxluo.20160412.104218 test-keys
SDK version: RK30_ANDROID4.4.4-SDK-v1.00.00
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.