I'm gonna repeat myself here, because I believe I am correct. Yes, you can combine a regular Sat. line with an OTA line. But I don't think you can combine OTA with the MODULATED TV2 output, which is what you are trying to do.
You can and I do, it just takes a lot of trial and error to get working clearly.
Is the diplexer crap? All the amps and diplexer are from Radio Trash.
Use a combiner, a diplexer is for something else.