I don't know if any of this helps - I just picked up a Le Potato this week and installed Armbian Hirsute on a 32gig Libre eMMC - I went through all the nightmares I've googled/read including the uboot button/USB cable/USB Burner software/Parse error stuff etc.
I did the following to get Armbian Hirsute headless installed on eMMC (the last bit may or may not save someone some time):
Downloaded the Libre Computers-suppled Ubuntu Bionic Headless image for aarch64: http://share.loverpi.com/board/libre-computer-project/libre-computer-board-aml-s905x-cc/image/ubuntu/libre-computer-aml-s905x-cc-ubuntu-bionic-headless-mali-4.19.55%2B-2019-06-24.zip
Burned the image to SD, booted, ran the steps in the eMMC Flash guide provided by Libre: https://docs.google.com/presentation/d/1gP-8njKQg6WE3p9HOU55m39NyLyq6IBa0Ukww5N15IU/mobilepresent?slide=id.p
It dawned on me after doing the above, booting Libre-Ubuntu from eMMC, re-starting from SD and then trying to dd the Armbian image to the eMMC, trying to wipe the eMMC, doing a cursory review of installing uboot manually on the eMMC, etc. - If I just get the details from the lc_redetect_emmc (utility provided by Libre to move from SD to eMMC after installing/booting from their image on SD), flash and boot Armbian via SD, insert the eMMC after boot up, and re-scan/detect the newly inserted eMMC - I avoid the Android boot/eMMC boot priority and, in theory, would be able to use armbian-config to transfer the files to eMMC after boot up.
This is the last bit that might save time/help:
lc_redetect_emmc looks at /opt/libre-computer/model/aml-s905x-cc/dtb/device.map for device node and device driver. node = d0074000.mmc and driver = meson-gx-mmc (this device.map file is available if you follow the steps at the top and burn the libre-provided ubuntu bionic image and boot it form SD - you don't need it to do the steps below. I also do not know if the Libre utilities are available separately - didn't bother looking)
Once booted into Armbian - attach the eMMC, (avoid short circuits) run: "echo -n d0074000.mmc > /sys/bus/platform/drivers/meson-gx-mmc/unbind && echo -n d0074000.mmc > /sys/bus/platform/drivers/meson-gx-mmc/bind"
The eMMC is detected (at least it was for me and it wasn't listed before I did the above) should be seen when running "lsblk -dno NAME,SIZE" (you should now see /dev/mmcblk1 in the list). Use armbian-config to install/boot from the eMMC.
