thanks doggyofone - I saw your post but it was for a different model.
I have progressed.. I still had the ''original'' 102K4 firmware on the M8, so I looked for newer and couldn't find an official firmware - but I did much reading and installed the ReMiX 115K4 firmware - which works well and also allows me to boot from SD card.
EDIT: link to ReMiX here - [ROM] RemiX 115k4 >>>s802 -
FreakTab.com
I literally just tried rebooting the media player with libreelec on SD card and it boots, does some checking and gives me a lot of error messages but the main error message seems to be with thinking the SD card is read only.
repairing filesystem...
?? invalid argument
Read-only file system
.ext4: Read-only file system while trying to open /dev/mmcblk0p1
write-protected; use the -n option to do a read-only
fsck failed. Yout system is broken beyond repair
please re-install LibreELEC
so this is on a known working SD card that I can boot to libreELEC on my s905 media box.
more reading.
EDIT: I cannot format my SD card now so probably bad - I don't have another one to test. Will have ot buy on on Thursday (payday).