Just for completeness, here is the last piece of my puzzle: Although my changes had the BIOS installer working correctly, the EFI installer would fail to install grub. What I was needing was to create grub.list.binary in config/package-lists:
grub-pc-bin grub-efi-amd64-bin grub-efi-amd64 With a .list.binary suffix, it allows the packages to be present in the deb pool on the installer medium if it NEEDS to be installed, but not install it in all cases (like BIOS when it breaks things). Now my ISO template (https://github.com/mmguero/deblive_blank) creates an installer that works for both EFI and BIOS. -SG -- Seth Grover
