Happy to help. The media button allows audio from the HDMI input on the rostrum to be mixed into the chapel audio. The idea is that you can play a video on an attached laptop computer and the audio will be heard by those in the room. For success you will need a HDMI splitter. (I can provide a recommendation on what works for us.) From the laptop the HDMI connection is sent to the splitter. One output of the splitter goes to the projector. The second output from the splitter goes to the HDMI input on the rostrum. If you press the media button then the HDMI input will patch in the audio to the chapel mix.
We do not use it. We run one more cable. This goes from the audio output of the projector to the RCA inputs on the left side of the podium. This input has a volume control attenuator. This is also a direct connection to the audio mix that bypasses the need to pull audio from the HDMI cable. When the presenter plugs in their laptop the computer usually sets the audio output to the HDMI port. I then just tell the presenter to adjust the knob on the podium to the desired volume level. It is easily within reach and has more dynamic range. Everyone knows how to use a volume control knob.
The QSC audio processor has volume controls on that panel. The min and max of that control is set by the system programmer. On our system we have found that this is a much smaller range than what the system is capable of. Like I said the knob for our system has been programmed to have greater range and works better. It also eliminates the need to coordinate setting the volume between the speaker / presenter and the person that has access to the control panel.
For more info on our setup see
http://www.federalwaystake.net/Hosting