working on this today. was able to get it to work this way. add the following to end of the pinballx.ini file
[System_2]
Name=Pinball FX3
Enabled=True
SystemType=0
WorkingPath=C:\Games\Pinball FX3
TablePath=C:\Games\Pinball FX3\data\steam
Executable=Pinball FX3.exe
Parameters="-table_[TABLEFILE]"
LaunchBeforeEnabled=False
LaunchAfterEnabled=False
LaunchAfterWaitForExit=False
still tweaking other settings based on my 3 screen cab set-up, but it works....