We are working with a multipurpose room that is used for lectures and showing movies. It’s messy from a control standpoint, but we can use an A/V receiver and
switch to a separate audio input during computer presentations, such as spread sheets, but this does not allow talking over HDMI video. There is a projector and a Large screen TV, each with external speakers, possibly showing different sources.

I’m not aware of a ‘box’ that will allow me to mix an audio feed with HDMI audio. Fortunately we don’t need to deal with HDMI-ARC. Using the A/V receiver we can easily accommodate whatever the presenters show up with, such as AppleTV, Airplay 2, Bluetooth, or a direct input. It’s the audio mixing that is the challenge.

No easy way to do this but it is possible. You need a video mixer or something that can delay the video to the monitor. You also need a good digital mixer with a good number of inputs and output that can be assigned. You can't do it with a receiver but you can do it with a preamp/processor and you insert the digital mixer between the prepro and mixer. If it is a 5.1 system you need at least 8 inputs and 6 outputs that can be assigned.

The 5.1 from the prepro goes into 6 of the inputs of the mixer and routed to 6 outputs of the mixer. Say you have 2 mics. They can be mixed into the 5 channels. you wouldn't mix it to the sub.

On the video side many video mixers have the ability to delay the HDMI video. The output of the receiver's HDMI would go into the video mixer, delay is typically needed as the digital mixer will add a little time. Output from the mixer goes to the projector.

There is more pro equipment to do this but you better have 6 figure budget.

For auditoriums and similar areas are often not surround sound and usually stereo or even mono. Then get an HDMI switcher that strips the stereo audio and add it to a mixer to go to an amp. Other than that it is probably easier and less expensive to add a separate system for the mics. Then the surround and the mic can both be used. Some companies even make an HDMI switcher with a mic input. Often used for this type of application and conference rooms.

Yes, a separate mic system would be the simplest from a design and control standpoint.

I am hoping that someone can suggest a ‘box’ that I haven’t discovered. I could use the receiver as an input switcher that integrates Bluetooth, etc., and ignore its internal amplifiers, exporting audio to external amplifiers, mixing the microphone along the way. Maybe there is a receiver that allows me to patch the front channels through a simple resistor network that mixes. This could be repurposing an eternal equalizer patch. In the old days this was fairly common on stereo receivers.

How many speakers will; be used? If the room is fairly large, does it really need to be a surround system? It would seem very difficult to provide a real surround experience when the listeners are far from some of the speakers.

If you agree about the idea that it doesn't need to be a surround system, this should be fairly easy since audio extractors for HDMI are pretty easy to find. If several HDMI sources will be used, a 2 channel receiver like the Denon DRA-800H can be used as a switching device, sending the audio to a mixer so mics, BT, Airplay, etc can have their own channels in the mixer.

Would the MGX series of yamaha mixers help? [Link: ca.yamaha.com]

It’s not a huge room and 5.1 is practical.

Might be practical for small surround systems, but as soon as you add the need for a mic and mixer, practicality goes out the window.

This is a senior citizen facility. The sight of all those buttons would probably induce strokes. 🙈