Hello Michael,
It may be a bit late, but I wanted to let you know that Launchbox does not append the final "File" part to the command line when you are already using %romfile% somewhere in the parameters.
The Sample Command includes it, but it is false, it is not passed in the command line.
I just tested it on 9.3 using a simple batch file that outputs all arguments it receives (just write "echo %*" in a .bat file to test).
So your %romfile%,4 solution is correct and would work if you test it.
Regards,
Patrick