You can locate your model at the bottom of the DVR my guess is you might be using the AMDV5M8 or 5M16 DVRs, That is a newer version of the 7108-AI DVR.. I personally don't understand how a package would be put together with cameras that wouldn't work in the native format for Amcrest..
So on my 7108 I had to change the cameras to 3mp to get it to work. Down side to that is the audio didn't work in the camera on 3mp and only works in the CVI format..