I use a small audio mixer to supply audio to my GH3. The camera audio is set to level 1 to avoid using the camera's preamp. I can't seem to monitor the audio though the camera's headphone jack. When I plug my headphones into the mixer's headphone jack, I get strong audio. I have tried various settings in the camera with no success. When I play back the video, the audio is there but I still would rather monitor it during the shoot. Am I missing a setting? Suggestions?