The Filco is a very nice keyboard. At one time they provided competent support so it might be worth asking the Filco people about the USB/PS2 converter dongle. I don't think they work with the combined Mouse/Keyboard PS2 socket as used on the -70K (at least, I've not been able to find evidence they work) but they might have some insight.
If the POST process is hanging at item 95 when the keyboard is plugged into a USB port, try a different port (i.e., USB 2 if USB 3 doesn't work, or vice versa, or sometimes back panel ports won't work but front panel ports will, or some variation). This seems to be a bug in the BIOS and my experience has been that the ports that recognize a keyboard or mouse during POST seem to change among various BIOS releases.
Also, verify that all of the "fast boot optimizations" are disabled.
