@Andrew-Seals The standards for the ipxe boot loaders are:
BIOS: undionly.kpxe (kkpxe only if you have problems with kpxe.
UEFI: ipxe.efi (or sndonly.efi if you have problems iwht ipxe.efi)
If your environment has to support both uefi and bios systems and you have a Windows 2012 or newer dhcp server or a linux dhcp server you can setup dynamic boot file assignment by following here: https://wiki.fogproject.org/wiki/index.php/BIOS_and_UEFI_Co-Existence