Regarding your talk-back Mic. If you need it for talking to your Overflow, then you could feed it to the Room Mic Group. You will also need to feed your Room Mic Group into the T-Loop and Overflow Matricies along with your LR Buss. This way they both get your main mix as well as the ambience from your room mic. In our main sanctuary we use a stereo pair of room mics for ambience for our video, CD, and Hearing Assistance, and these get mixed in with everything else.
There are several ways to go about the Overflow and T-Loop situation. You could set up the 25-44 channels to mix separate mixes for the hearing assistance and overflow rooms and send that mix to a Mono Aux or Mono Sub-Group then to the Overflow and T-Loop Matricies. This is just a suggestion. This means you can mix separately from your FOH mix with different channel processing.
Sorry about the rambling…Things just keep coming to me.
Scott
