I created a bootable usb drive in disk utility
then ran diskutil list
to find the identifier
/dev/disk2s1
in my case
make sure to unmount the drive
then dd
sudo dd if=debian-9.6.0-i386-netinst.iso of=/dev/rdisk2 bs=1m
yes, use rdisk...
.
when booting the asus, press escape to boot from usb
I did not get any of this to work with a sd card. this could be due to not properly formatting the sd card or not booting from the card. I'm not sure the asus will boot from sd, only usb or hdd.