Once again, thank you, Armond. I think I will try the path of least resistance first. I will pick up a splitter, and maybe a terminal if needed, and try avoiding the coax out from the MoCA to the STB. I just saw STB Out on the rear of the MoCA, so naturally I assumed this would work.
Hopefully I can give this a go tonight, and will report back. The more I read that second link you provided, the more I think this is indeed the issue. But if I change the setup and still see the same problems, I'll move on to the other steps you suggested and come back with details soon.
Thank you again for your help here.
And to clarify on this point:
Coax carries both TV frequencies and Internet frequencies. What I think your description signifies is (1) that in the room you discussed in your original post, you have a coax jack; that (2) you have run coax from that jack to the MoCA adapter; that (3) you have run another coax from the adapter to the TV. Since the TV is working correctly, it's fair to assume that the MoCA adapter is also working correctly.
...my saying coax from the pole was perhaps too simplistic and incorrect. I'm just reiterating that the line coming into the back room is split off at the house, and not from the router or downstream from it. Just wanted to make sure, in case the symptoms described might have indicated that the issue could be a result of the coax line in the back room not being connected to the router in any way (as Actiontec's diagram had shown). I think it's clear this issue is moot, though. All functions for the STB seem to work fine, but I do not have a landline phone, nor the DVR so I can't comment specifically on those two. However the guide and other menus all appear to be working just fine.