First step was to mount the Digitrax TSMK under the layout and connect the double head dwarf wires and ribbon cable.
Next step involved programming the individual heads of each dwarf signal into JMRI. So for the double head dwarf this means adding the the two heads individually for each mast, and each head requires two turnout positions from the SE8C boards. So one double head dwarf requires four (4) turnout positions (not a physical turnout) from each SE8C board.
Once the heads have been added these can then be added to make a mast (JMRI term for the double head dwarf) and then JMRI can go about its thing and change the appearance of each aspect.
Presently I'm using the pre-loaded JMRI AAR-2 Signal aspect table as it's fairly close to the Conrail Signal Aspect Chart - 1988 that I eventually want to add to JMRI.
I've also made a short clip to show the different aspects loaded in JMRI and running through the double head dwarf.
I also managed to connect a single dwarf too, now the Reading area of the layout has its dispatcher controlled signals installed.