ok. I did a few tests. I can boot successfully from the SD only with if the SD card as the image as per post #1 (including the rename of the boot_autoscript to boot.scr). Deleting the s805 script makes the SD card unbootable and it gives me the error in mount_flash error at start up.
If it can help my device is the X8H
I was tempted to try to remove the aml script instead of the s805 but I m not so brave