OK, as promised, I captured the west coast feed of an ABC show and I was able to do Nashville
I extracted the audio as 16 bit WAV files and brought them into the audio editing program that I have.
Here is what the 6 channels looked like for the hour (commercials included):
As can be seen, the center channel (third waverform from the top), has a level that matches, or exceeds the top two L/R channels. The average of the three channels is -6 db.
I listened to the center channel, on its own, and heard no issues with it at all.
I even did a special mix whereby I placed the center channel into both of the channels of that particular stereo wave file and reduced the level by 3 db (standard practice when mono audio is placed into both channels). I then mixed the L/R/Center into a single stereo wave file and gave a listen to the beginning and the recording session at the end of the program.
There was nothing wrong with the audio. The center was crisp and clear and easily heard.
If there is a particular section of this episode that anyone would like to hear, let me know and I'll extract that stereo portion of the wave file and make it available. Please give the approximate time the section starts and what it is about, so that I can find it.
If need be, I can make an AC3 file of a particular section for listening to as well.
In conclusion, in my non-expert opinion, I heard nothing wrong with the audio that ABC is supplying to the west coast affiliates.