If you run a command like this:
java -jar dist/Dguitar.jar files/bends.gp4 "files/4 hands.gp4" "files/ritmos varios.mid"
on a single line and keeping the quotes (") DGuitar will open those files at start up.
Make sure you also check the "Arrange Cascade" and "Close All" in the "Windows" menu.
For more info download the latest DGuitar-dev and see the README, NEWFEATURES and TODO file
Let me know if you find any bugs