Thanks Gents, Having the bios password proved to be a game changer. My previous experience with a firebox M400 required opening the case to add an SSD with a working pfsense installation and flashing a Lanner unlocked bios.
By contrast, the M570 install was absolutely painless, and I was successfully able to install pfsense after booting from a USB flash drive. I did have to get into the bios to enable USB booting and modifying the boot drive priority. I was planning to swap out the processor for a low power Xeon but I'll let that project sit on the back burner for now.
Many Thanks!