It's been a while since UEFI comes around. So that, it's no longer make sense to stick to Legacy or BIOS mode when the system is able to utilize UEFI.
The default bootloader as of current latest Win81pese is Grub4Dos and it's been a long time since Dos replaced by Windows.
Here, I would suggest to port Grub2Win as additional bootloader option, since it is based on latest Grub and supports both 64 and 32 bit UEFI
in addition to legacy bios. Below is the content of grub2win.zip file downloaded from Grub2Win source forge project page.
If Grub2Win is selected as boot loader, grub2 would be default loader for both UEFI and Bios mode.
I think it wouldn't be too hard to port Grub2Win as additional bootloader since it's mostly the similar to Grub4Dos.