Hi. You are not the first person that mention this thing.
https://forums.vmix.com/...-still-callers-have-echo
https://forums.vmix.com/...l-Participant-Hears-Echo
https://forums.vmix.com/...king-with-Rodecaster-Pro
Saying that professionals use headphones and un-professional no,my personal opinion is that cannot help to find the solution. As you said other broadcasters have no problems with this. In the posts i send you,there exist solutions and an obvious thing. The mix minus/echo cancelation in vmixcall is not so "professional" compared to zoom or other programs like skype that i personally miss allready. Ok maybe the most High Audio quallity is true,but in real world scenario for un-professional (not high budget streamers because everything is how much costs when it comes to equiment) zoom/skype way,work better
I work in a small tv station in Greece. What you describe is same like my scenario. In the studio i send the audio return via a tv hdmi audio from Vmix Fullsreen out.
My talents dont wear any headphone. Sometimes for example before 1,5years we had elections and in the studio we had 5-6 people with 1 mic per person. So in theory 5 mic to make "echo". In practice our show presenter can wear a headphone when we have a videocall or phonecall. But what for the other guests? They will not hear the videocall/phonecall or we are obliged to have 5-6 wireless headphones per day (in order for changing for health reasons the headphones cover or say guests to bring their headphones) ?
Measures that worked for me
1.Inside the studio i send BUS G that is gpu-->hdmi out-->tv in the studio. In this BUS i send the audio from callers or phone call
2. In any of the mics i select BUS F and i send it to videocall/phonecall. Skype was running in a separate pc in which via ndi tools-->webcam i send video/audio from main vmix pc and back to main vmix pc from skype i take ndi feed per person
3. The speakers in the studio should not be too close in the people table and not too loud. Set them in a level that anyone can hear and not too loud.
4.In any mic and skype feed/phone call audio i put this https://www.wtautomixer.com/ vst3 plugin. Yes it costs 160$ but it work. It has 7 days trial so you can test it, if also work for vmixcalls. Anyway this plugin in our studio without any serious soundproofing,with echo and it does a great job.
5.Skype close was for us in the end of our season shows. So for now i hadnt yet the oppurtunity to do with same setup in real show conditions 2-3 vmixcalls same time to see what happens. I hope that i will not have problems at mid of september we start again new shows. Because as un-professional to have headphones per guest is not in our budget. About mid september i will be able to test it.