Error: variable 'prefix' isn't set

Trying to install UCS on an HP ProLiant DL160 G6 server. As best as I can tell, it does not support UEFI. Anyway, when I try to install via USB (no CD/DVD drive) I get the error message that is my topic. I have successfully installed Win2016 Hyper-v Server on this system, but am wanting to try out UCS on bare metal (not in a VM).

All related topics that I have found stem from needing to disable UEFI. As best as I can tell from looking at the HP BIOS of this system, it either doesn’t support UEFI or I am unable to locate anything in the BIOS enabling me to turn it off. Being a bit older (G6 is gen 6 and I think they’re on gen 9 now), lacking UEFI support isn’t that surprising.

Any suggestions? Thanks!