Got it working with 9.3 (mostly)!
My solution (more of guess and check) was to:
1. Load the ISO, get to the installer screen. Edit ('e') the commands and add
Code:
kfreebsd_module_elf /boot/kernel/xhci.ko
after the kfreebsd line in the grub loader. F10 to boot, install.
2. Reboot, and once again edit the commands and add
Code:
kfreebsd_module_elf /ROOT/default/@/boot/kernel/xhci.ko
after the line for the ispfw.ko. F10 to boot. It will return error 2 if the USB(s) have not been recognized yet. After they show up on screen, retype the boot location (zfs:freenas-boot/ROOT/default).
3. Uncomment xhci_load="YES" in /boot/loader.conf
Still needed to tell it to boot to the right place after updating the OS. After all that trouble, this board may be repurposed to a router and I'll get a different mini-ITX for the NAS.
Hope this helps someone trying to get this board to work.
On a side note, will XHCI be enabled by default in FreeNAS-10?