I have done many similar events.
FYI - I have been doing audio/visual work since the seventies and have much experience in sound and video projection systems. I will try to explain the basics of what to do in order to have an effective meeting. Be warned, this will turn into a physics lesson. After lots of practice, you should have no problems.
Most of the potential issues deal with getting sound in the physical room to the virtual listeners and sound from the virtual listeners to the physical room. Get with your local sound or A/V person to go over all of this.
You need one computer to be the master. This is the one that runs the GoToWebinar as an Organizer, projects PowerPoint and webpages, projects the local webcam, and has sound coming in and out. For this I am using an 8-year old Mac PowerBook.
You might have a second computer logged in as Organizer to facilitate answering questions, looking at the attendee list, promoting people to panelist, etc. Make sure this second computer (and any other computer in the room) has its microphone muted as well as its speakers turned off.
Sound can be tricky. I often use two (or more) hand-held wireless microphones. The local presenter (in the room with the audience) uses one, and the other is available to capture people in the room audience who want to ask questions.
It is important to note that people HAVE to talk into a microphone in order for the virtual audience to hear them. This is tricky when the physical meeting room is not large enough to really require microphones, or when folks in the audience think they can talk loud enough for the people in the room to hear them. The problem is that if someone does not talk into the microphone, the virtual audience will only hear too much room noise (echoes) and not enough of the person speaking. It is imperative to encourage (warn sternly) the audience to wait until a microphone is in front of them before they speak. You need one or more really good microphone handlers who can move about the room really fast to capture people in the audience speaking. Speed is key to keeping the momentum of the meeting going, and keeping the virtual audience tuned in. Larger physical audiences require more microphones and more microphone handlers to keep them moving. These microphone handlers need to be able to politely say "wait until I get to you with the microphone."
Do not turn off ALL of the microphones, even if you take a bathroom break or a break for small group discussions. The virtual world might panic if there is no sound at all coming out of their speakers. The sound of commotion in the room will let them know they are still connected. Leave at least one microphone turned on all the time, unless you have a virtual speaker talking, then you can mute (turn off) all of the microphones in the physical room.
Setting up the sound system. Run all of your microphones as well as the output of the computer into a sound mixer. The output of the sound mixer goes to the local room as well as to the main computer. I usually have the projector, sound mixer, and main computer all next to each other.
On the output of the sound mixer, I usually send the Left Main output to the local sound/speaker system. The Right Main output of the sound mixer goes to the input of the computer.
I used to use the Blue Icicle, but now use the Shure X2u to convert the analog signal coming out of the sound mixer and turn it into a USB signal that GoToWebinar sees as a single external microphone.
On the sound board, all of the microphone inputs are panned (assigned, routed) to both Left and Right, which means an equal amount of each signal is sent to both the house sound/speaker system as well as the input of the computer. The sound coming from the computer is panned to only the Left main output. You do NOT want to send the output from the computer back into the computer.
I come out of the headphone jack on my computer using a special cable to go into a stereo input on the sound mixer. On the computer end of the cable, there is a 1/8" mini stereo connector that fits into your computer headphone output. The other end of the cable depends on the inputs on the sound mixer. My mixer has two 1/4" connectors for the stereo input. They might be listed as "1/4 TS,” or might be called "phone plugs," since this was the connector the old switchboard operators used in the old days to patch telephone calls.
Some sound mixers might have RCA connectors rather than the 1/4" connectors. RCA is a generic term that refers to the connectors we used to have on record players as well as most stereo equipment.
Here is an example of a cable that will connect the output of the computer to the input of the sound mixer.
https://www.sweetwater.com/store/detail/CMP159--hosa-cmp-159-10-foot-3.5mm-trs-to-dual-1-4-inch-ts-c...
For the visual images (PowerPoint. Webpages, etc) being projected in both the physical room and virtually. Connect a projector to the main computer. I then set up my computer so the Projector extends the desktop as if it were a second monitor, which allows you have different things on the projector and the local monitor. You do not want mirroring turned on. I set it up so the projector is considered to be my second monitor. I keep all GoTo windows on my primary monitor. In GoTo I tell it to share the second monitor, which means that whatever I drag to the second monitor is what both the physical audience as well as the virtual audience will see.
You can stack multiple windows (one in front of the other) on the second monitor. I usually have a web browser in the background, which is hidden by the PowerPoint when it is showing. Hitting the ESC key during PowerPoint will temporarily end the PowerPoint show on the second monitor, thus revealing the web browser behind. To restart the PowerPoint, I hit the little button in PowerPoint that starts the show from the current slide, and then you are back to showing the PowerPoint show.
Set your screen saver on your computer to off and energy saver to 3 hours. That keeps the computer from falling asleep during the presentation. One place I work has an internet timeout after about two hours, which means the Internet access will shut down if I do not click something in a web browser. GoTo Webinar just stops abruptly. Even if I am not using a web browser for this particular webinar, I have to remember to click something in a web browser every hour or so.
A note about control. - Only one computer program can respond to the keyboard and mouse at the same time. You may be able to see the web browser, PowerPoint, and the GoTo Webinar control panel, but only one of them will be “active.” This is frustrating when during a PowerPoint show you click on the GoTo control panel to check a message, then all of a sudden, your PowerPoint won’t advance to the next slide. You have to click back on the PowerPoint window to make it active, which will then transfer keyboard and mouse controls (as well as remote clickers) to the PowerPoint program.
PowerPoint tries to hog all of the control while it is showing a presentation. To get a different program to be the active program, you might have to click on the top edge of the GTW control panel, then click on the other program that you want to be active. This might not change what folks see on the projector, but it changes the "active" program. This takes the most practice, and a cool head when things do not seem to be going right.
Practice, practice, practice.
