linux (loop)/boot/isolinux/linux knoppix64 ....
With "ISO install to HD" you don't need the cheatcode "knoppix" or "knoppix64"; therefore you have to omit this cheatcode in this installation mode.. You already did your decision which Kernel you want using "../isolinux/linux" or "../isolinux/linux64".

By the way: the cheatcode "nostartsound" isn't supported within the new Knoppix versions.