At the entrance - several speakers, at the exit - mixing into one channel?

Question

macOS

What is required: ensure that several remotely connected people are brought together into one audio channel (with the ability to adjust the volume, turn off and add “tracks” from files, for example).
Those. everyone speaks (sings, raps - it doesn’t matter) into his own microphone, and the operator mixes and receives one stream at the output, which can be broadcast.
How do they do that?
My considerations
"Remote microphones" may be needed for both Mac OC and Windows or Linux, so they are seen as a page with a Flash application.
If we continue to think in this direction, we could probably use something like smotri.com, if we take only the audio stream from there (suppose it will be there in RTMP) and find software that could receive and mix RTMP streams.
Next stop...

Answer 1

sound transport and mixing are different tasks. the idea of ​​mixing RTMP streams sounds untenable. what part do you question: transport or mixing?

Answer 2

www.bigbluebutton.org/ solves the specified problem.