Can't install on AOpen MP965-D (non-UEFI)

[JesseWV]

I am trying to install OPNsense on an AOpen MP965-D but I can't get the installation media to boot from USB.

I prepared the USB stick with Rufus and OPNsense-18.7-OpenSSL-vga-amd64.img

With the USB stick inserted, the box immediately hangs before post. If I insert it after post, it immediately hangs as well, even in the BIOS menu.

I can insert the same USB stick plainly formatted without the OPNsense image on it and the box behaves as normal.

I've tried installing via disc only to discover it only has a CD-ROM drive which will not hold the entire uncompressed DVD image OPNsense-18.7-OpenSSL-dvd-amd64.iso which is  939MB so that's out.

So I'm thinking the problem for the USB drive is that this board does not support UEFI. Is UEFI required to install OPNsense?

If so, are there any other options?

[JesseWV]

Just for reference, nothing I did regarding the USB stick or disc worked. 

I was successful by putting the hard drive into a laptop, installing up to the first reboot and then putting it back in the MicroPC.