The system was running Android (unchanged) before. I understood I needed to do the toothpick method to boot from SD card, maybe I was mistaken.
I understood from this thread that for the universal image, a u-boot file would need to be used, and above in this thread, it was suggested to someone else to use u-boot-odroid-n2 on an S905.
Andrew.
Update: It seems that the image does actually boot with odroid-n2 u-boot, but no HDMI out. Network is working. (And yes, no toothpick was necessary to boot from SD)