DigitalEngine

Ok, I figured it out.
Actually it works "out of the box" so to speak in a standard configuration.
Set all three monitors to the same resolution (1980x1020), full screen off, selected LMFCD=Camera+RMFCD, and resolution 5760x1080.
 
However, I am using 3 differing monitors with differing native resolutions. I suspect that if I want to use each monitors native resolution I will have to create a custom \Config\MonitorSetup\custom_monitor.lua file?
 
My ultimate goal is to duplicate the Shkval and ABRIS displays on monitors for spectators to view, while operating the DCS Ka-50 in VR if that's possible.
 
[edit]
I found this thread, buried in the A-10 bugs forums.
Multi-monitor set-up guide & help (unofficial)
and this post https://forums.eagle.ru/showthread.php?p=2616874#post2616874
Don't know if it's out of date, but maybe it'll get me started.

As a very late update Solution, works as intended.
The Su-25T uses the PRMG system only.
AFAIK, only Russian military airfields have the PRMG system, and only the following, at least the last time I checked.
Krasodor - Centre, PRMG 38 - *Runway 09 Only
Krymsk, PRMG 26 - *Runway 04 Only
Maykop - Khanskaya, PRMG 36
Mozdok, PRMG 22
[*Must be the active runway!]
And of course as the Su-25T being a Flaming Cliffs type DCS module, one dose not select the
particular PRMG frequency, but only selects the landing sub-mode.
For additional info, PRMG notes here, and Russian PRMG & ILS Landings post.