Can you tell a bit about your system? Is this an UEFI motherboard? Or BIOS? If UEFI, did you disable secure boot before trying to install KaOS? Do you use GPT or msdos partition table?
To know a bit more what is going on, please pastebin /var/log/installation.log and /var/log/grub-installation.log (might need to use the Live ISO to access those logs).
If everything installed just fine and if I read correctly that Windows8 is just missing, you can rerun:
sudo grub-mkconfig -o /boot/grub/grub.cfg
The output will show if all Operating Systems were picked up.