You want to run the GUI in debug mode, run it like this:
/Applications/calibre.app/Contents/
calibre-debug.app/Contents/MacOS/calibre-debug -g
And if you want to turn off the splash screen, do this:
Code:
echo '{"show_splash_screen": false }' > ~/Library/Preferences/calibre/gui.json
Backup gui.json first, as that command will overwrite all settings stored in that file. Although, I doubt this has anything to do with the splash screen. Most likely the calibre main window is starting up on an external monitor or secondary screen.