If you want to understand what should be happening under a normal installation:
Installing "multiboot" (i.e. pressing the hidden reset button while powering the device) runs the script aml_autoscript
That script sets some uboot environment variables that are used by subsequent boots
The boot process for these boxes is to use the original android uboot to intiialize the device and then hand off the boot process to the u-boot.ext from armbian.
This is done in the script s905_autoscript (or emmc_autoscript).
Which then essentially just runs (for emmc):
if fatload mmc 1 0x1000000 u-boot.ext; then go 0x1000000; fi;
(or "mmc 0" for SD card).
The chainloaded u-boot then boots via the information in the extlinux/extlinux.conf file.
Current Armbian uses extlinux to load, not uboot scripts. I can't help you unless you are willing to follow my suggestions, which you seem to not want to do.
