They are Cd/DVD ISO debian-installer images so you don't set them up like a standard pi sd card image. Have a look at the mini ISO images I made for raspbian - viewtopic.php?t=195162
, or you could boot the iso using uboot/grub (like I showed in the Ubuntu thread). Debian's generic arm64 kernel can be booted by the pi firmware, which makes things easier than Ubuntu's generic arm64 kernel (which needs uboot as far as I can tell).
The debian wiki seems out of date. A custom armhf kernel should not be necessary as pi support was added to the debian kernel in Dec 2015. So the armhf debian installer should work on the pi 3.
You might also like to read a bug I created which discusses the debian-installer on the pi - https://bugs.launchpad.net/raspbian/+bug/1723203
If you want to make an sd card image (like the Ubuntu server image), then the livecd-rootfs package is what is used in Ubuntu to build it. Ubuntu-mate uses the raspberry pi flavour maker to create their images. They use the same kernel as raspbian, so you could do the same in debian armhf. Raspbian build scripts are here https://github.com/RPi-Distro/pi-gen
. Doing it manually in debian is described here - https://www.debian.org/releases/stable/ ... 03.html.en
Lots of other build scripts kicking about the internet, but the standard armhf/arm64 debian-installer should be usable and I think are the best choice.