Download latest KitKat 4.4.2 stock firmware for MBOX S82 TV Box from here or here. To flash firmware on this box from SD card read this article.
Archive: MBOX_111k4_sdcard
Model: MBOX S81 TV Box
Image file size: 409 MB
Platform: Amlogic S802 quad core
Update file name: k200-ota-20141218.zip
Build number: k200-user 4.4.2 KOT49H 20141218 test-keys
Update file name: k200-ota-20141218.zip
Build number: k200-user 4.4.2 KOT49H 20141218 test-keys