Well last night as well as doing more track work I also programmed the first of the double head dwarf signals into JMRI and installed it on the Panel Pro - Panel.
First step is installing the signal heads into the "Signal Head Table" each head requires two of the turnout ports from the SE8C (not its not actually a physical turnout, just a port) so there are four consecutive ports for this on head, 577, 578, 579 & 580.
This is how the SE8C has the ability to drive all three appearances on each aspect including flashing too.
Next step is to create a signal mast in the Signal Mast Table, when you select a double head dwarf you add each of the signal heads as above and this then allows JMRI to drive both aspects (high & low) together to give the correct signal aspect.
And once completed I then loaded the signal mast which in this case has a user mane of RDG25W onto the Panel Pro - Panel and I was able to operate the signal from the panel by clicking on the icon.
JMRI is such a powerful tool, you can right click on the icon and bring up the list of aspects and change to any of them, or just left click on the icon and it will scroll through each on each mouse click.