Classroom sound loops with remote Connect faculty

I am trying to get advice from users who use Connect for webcasting in classrooms. We have three classrooms(webcasting one at a time) with a central office where video and sound from the classrooms are feeding into a host computer hosting a webcast. So our audience is live attendees and remote attendees with faculty teaching live in the classroom.

We would like to bring in guest lecturers via Connect so the live class and faculty can interact as well as Connect webcast users able to see and hear them. But, need advice on how to alleviate the sound loops in the classroom.

If we had the camera and microphones in the classroom connected to a classroom computer as host and projected on the classroom screen we would have no sound loops because sound from that computer, while going to the sound system, would only output the guest lecturer on the classroom speakers and not the microphone connected to it because the classroom computer would be muting the microphone sound while hearing the remote lecturer.

But, we host from a computer in another location and classroom sound and camera is hosted there. So if we log into the classroom computer as a participant in the meeting and project it on the screen for live attendees to see and hear the remote faculty, the clasroom microphone sound is also transmitted through the classroom speakers because near and far end sound are coming out of that computer, because they are a participant watching. Naturally that sound gets fed back to the webcasting office causing a big feedback loop.

Any suggestions on how to do this without having to put cameras and microphones in each classroom into the classroom computer? We need to run webcasts from a remote office.

I hope this is clear. If not, please let me know and I can clarify.

Thank you.