How does one 'add' a second console f/w to the flash on the PC164?
   
Each image seems to include a notion if where it gets loaded.  All we had
to do was simply run the firmware update program on the floppy that provided
the console software.  They did not overwrite each other.

   For both you could use a Qlogic SCSI controller I guess. The EB164 has a
   builtin ncr?

Yes, the EB164 has the on-board NCR SCSI, for the PC164 we used a similar chip
on the PCI bus, because the SRM knows how to boot using that chip.  Most of the
problems I had and other users had locally under NetBSD were related to the NCR
disk driver screwing up.  I remember one of the developers asked on this list a
couple years back if we wanted them working on Sparcs or the NCR driver for Alpha,
and I voted the NCR driver for Alpha, because I figured the people with Multias
would all be getting 21164 machines around now, and this was the single biggest
failure point for EB/PC164 boards.  I do not know what actually got done, there
may be much better code by now, I've been using DU and Linux for a while, mostly
because of X11, which apparently has moved up the NetBSD to do list also.  I look
forward to trying it out again on this platform, NetBSD was a good performer when
the disk did not lock up and refuse to restart.  In my case I was able to live with
less performance to get the graphical interface screen, my units all had displays.

Also note, when I bought mine, there were only two boards that were supported by
Digital UNIX, one was an S3 Trio as I recall (Diamond Stealth 64 I think) and the
other was the Digital graphics engine (PBXGB series), if you are considering going
back and forth between DU and NetBSD.  XF86 of course supports the S3 chips.