I am seeking a solution for push to talk microphones and mixer that will support a class room of 20 people with one microphone for every two students. The system will interface with a videoconferencing system. The videoconferencing system provides RCA audio out.
Consider the Shure MX412D or MX418D mic connected to Shure SCM810 or SCM820 mixers.
Also, read Audio for Distance Learning at Educational Articles.