As without serial console, I tried to integrate
load mmc ... into the Armbian boot script. Didn't work also with ext4load or putting it in separate lines
but ...
with the information of your posting how to access partitions I just copied the contents of the Openelec boot script into the Armbian one:
setenv bootm_boot_mode sec
setenv bootargs console=ttyS0,115200 boot=/dev/mmcblk0p3 disk=/dev/mmcblk0p2 consoleblank=0
fatload mmc 0:3 0x43000000 script.bin
fatload mmc 0:3 0x42000000 KERNEL
bootm 0x42000000
And this did work :-) :-) :-)
Thanks for providing the "hint"!
I had this nearly before, but with those two files on the Armbian partition and it didn't work.
I'll write a how-to, as I guess others are interested in this "dual boot" also.