This device could also run standard UEFI image.
Welcome to the Armbian Community Builds for Amlogic S9xx based TV Boxes
TV Boxes are not officially supported by the Armbian project. These builds are maintained by community members (like you).
To be able to boot Armbian SD card image and install Armbian to eMMC, use one of the methods to boot into upgrade mode. If you have most recent board revision (1.4 ->) then you only need to quickly press the function key (middle) 3 times in 2 seconds. Release and boot will proceed from SD card. Then use nand-sata-install utility to flash to eMMC.
Serial console:
Blue color line: Tool Pin TXD, orange color: Tool Pin RXD, black: Tool Pin GND
- can be picky for SD card type/brand