The EX will output an audio reference signal along with the colour bars but you have to turn it on first. Go to the Audio Set menu and turn on the "1kHz Tone" function. Then go back and press the "Bars/Cam" button under the handle. Now you should be outputting bars and tone. When you're done don't forget to go back to the Audio Set menu and turn the tone output off.
Yes, you want the reference tone at -20. Your audio should peak around there as well. But monitor, monitor, MONITOR! Use headphones or at least an earpiece. Just because the levels look good, doesn't mean you're not getting distorted audio.