Amazon's OS is based on Android, but alas, it is not Android. It is not KitKat or Lollipop, it's FireOS [insert version number].
Their newer devices offer no bootloader unlocking, making custom OS and/or kernels impossible to install.
Besides, each device requires its own ROM to function properly -- there is no single file that is able to work on multiple devices, much less so devices with different screen sizes.