I have tried other key combos without success.
OS X Help has this to say about that:
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Creating keyboard shortcuts for applications
You can assign your own keyboard shortcuts to menu commands in any Mac OS X application or in the Finder. This may be useful if, for example, one of the “global” shortcuts, which works the same in most applications, is used by one application for a different purpose. In this case, you can assign it a different key combination.
You can create keyboard shortcuts only for existing menu commands. You can’t define keyboard shortcuts for general purpose tasks such as opening an application or switching between applications.
To create a keyboard shortcut for an application:
Choose Apple menu > System Preferences, and then click Keyboard.
Click Keyboard Shortcuts, and then click the Add ➕ button.
Choose an application from the Application pop-up menu. If you want to set the same key combination for a menu command that appears in many applications, choose All Applications.
If the application you want to select does not appear in the list, choose Other and locate the application using the Open dialog. Some applications may not allow you to set keyboard shortcuts.
Type the menu command for which you want to set a keyboard shortcut in the Menu Title field.
You must type the command exactly as it appears in the application menu, including ellipses and any other punctuation. An ellipsis is a special character that looks like three periods. To type an ellipsis, press Option-semicolon, or use the Character Viewer. It may be difficult to know whether the command is written in the menu with a real ellipsis or with three periods, so if one does not work, try the other.
Click in the Keyboard Shortcut field and press the key combination that you want to assign to the menu command, and then click Add.
You cannot use each type of key (for example, a letter key) more than once in a key combination.
Quit the application for which you added or changed a keyboard shortcut.
Restart the application to see the keyboard shortcut in the application’s menu.
If you assign a keyboard shortcut that already exists for another command or another application, your new shortcut won’t work. Find the menu command that’s using it and reassign the keyboard shortcut for that item.
To remove a customized shortcut, click the Delete (–) button.
