Tvheadend

I have not looked at the code, but I would hope that it parses whatever it finds.

I assume you have already enabled the "over the air PSIP ATSC grabber" in Configuration->Channels/EPG->EPG grabber modules. ( Although the setting should only affect EIT and not the parsing of the channel info which should always be done regardless.)

On my system, it properly detects about 2/3 of the "local" channels, but no EIT data at all. (I only briefly tested with a direct connection to a TV, which saw all channel names, but seemed to only show now/next info.)

I do not recall for sure, but I seem to remember not even the cable channels were detected. (Did not care as they are all encrypted and I am only interested in "local" channels.)

I also seem to remember that I tested with using both network options of "ATSC-T" and "ATSC-C" and both had the same results. But that was long ago and maybe the code has changed by now. Have you tried using "ATSC-T"? It does not have a setting for QAM modes, but on my system it still managed to detect properly the QAM/256 modulation. Of course that may highly depend on your hardware and drivers...

I have been meaning to look into this, but never seem to have the time. I manually entered the missing channel info and then setup zap2xml to download EPG information and it has been working fine for a few years now. (hence not being a priority to fix...)

I made a change to the code, so it will check both CVCT and TVCT on ATSC-C. This seems to have fixed my problem.

I don't think this problem would be unique to me. The cable system transmits the local over-the-air stations with a Blonder Tongue AQT-8 transcoder, which simply passes the OTA 8VSB channels through to QAM.

I finally resolved some issues which were preventing me from making new builds for my ATSC system.

Can you post the changes you made so I can try it out? (I do not want to reinvent the wheel...)