Zoom Participants Not Being Heard Over Loudspeaker when 100+ connections (other Zoom callers can hear the audio)

When we have just a few Zoom participants everything works correctly - the Zoom callers can hear the audio from meeting room microphones and the Zoom callers can be heard in the room over the speakers. So by all indications our setup is correct - PC works, Windows setup is correct, Zoom setup is correct and connection to sound system (thru a sound board) is working correctly.

When we have 100+  callers we have been experiencing an issue where the Zoom callers can no longer be heard over the loud speakers. The users are being un-muted and asked to speak - they can be heard by other Zoom callers - just not over the loud speakers.

We have not tried using Host/Co-host setup which is our next step. Is there any other experience with this happening and/or recommended setup to try differently.