scook, I'm running X2a build 351.
I should have mentioned that I have had this previously working as intended and could send midi data to it no problem. It's a recent development that it will not appear in the synth rack.
In the plug-in manager -> plug-in properties for Artillery II, I have 'configure as synth' and 'enable mono processing' checked as the only two boxes. I've tried it with 'Enable as plug-in' both selected and unselected, doesn't make a difference that I can tell. When I go to details from the same view, I see
'Is Synth: No'
'Supports Event Input: Yes'
'Supports Event Output: No'
which is what I would expect. I don't think the registry tweak will help, as it is not sending midi data.