I am very interested in purchasing a Dahua Tribrid DVR. The ability to reuse some existing analog cameras and try the newer CVI type of cameras and IP cameras to boot. 
  
I noticed that there are generally 1 audio input and at the most 4  audio inputs on the Tribrid DVR's. 
I need to have audio with video on my system. I looked at the setup for a few models and there is an internal and audio input option for each camera. I can not find a HDCVI camera with  built in mic except for PTZ models. If you can port audio inputs  to multiple  channels that would work but I can not verify if that is possible, eg.  audio input 1 connects to channel 1 and 2  audio input 2 connects to channel 3 and 4 and different variations.  
  
also can someone give an explanation  of "reuse audio in and out " for 2 way comms 
  
thanks in advance.