Interpreting and GT console

I'm an interpreter trying to set-up a GreenTerp Console. The install instructions on a Mac tell me I need to set the keyboard shortcut for mute / unmute audio to shift-command-L, but the system does not register the L. There are some letters I can type, but the console doesn't function as it should, and some letters where the system tells me this is a shortcut already in use. Any ideas?