I have this problem too.
all 12 mics are mixed within a Biamp Tesira DSP, one line level output from the Tesira to Mic1 input on the COdec pro. The instructions I found said to lower the db level of the mic1 input using the audio processer within the web portal and to turn the phantom power off (also in the audio processor). I'm still showing all 8 mic inputs as inactive however.
I know I'm getting audio out from the biamp as I have a meter setup on the output of the programming and see the mic audio move when the room mics are being used.
I'm wondering if I need to connect a standard mic to the input as mic level, do the audio "sound check" from the settings and maybe that will activate the mic1 input. After that, I could make the setting changes to line level input. Only problem with that is my codec is in a rack 1 floor down from the actual auditorium.
I'll do more testing and reply here.