This is a short post detailing the install of Debian on the PC Engines APU2 using PXE.
First of all you'll need to ensure you are running version 160311 or newer BIOS. You can find the BIOS update details here. If the PXE options are missing then there's a good chance you aren't running a new enough BIOS!
Connect to the system's console via the serial port using a baud rate of 115,200. I typically use screen on Linux/macOS or PuTTY on Windows.
Start the APU2 and press Ctrl+B when prompted to enter iPXE, or choose iPXE from the boot selection menu (F10).
Attept boot from PXE using DHCP:
If all is well you will get to the "Debian GNU/Linux installer boot menu" heading, press TAB to edit the Install menu entry.
This should bring up something along the lines of:
> debian-installer/amd64/linux vga=788 initrd=debian-installer/amd64/initrd.gz --- quiet
You'll want to define the serial console by adding the console parameter to the end (and preseed parameter if used):
> debian-installer/amd64/linux vga=788 initrd=debian-installer/amd64/initrd.gz --- quiet console=ttyS0,115200
Press enter and you should be on your way!