Tivo S2 not receiving cable box signal

My aunt moved to a new house, so I volunteered to help her set up her A/V stuff, which includes a Tivo Series 2.

She has Comcast, which has given her a super tiny Motorola cable box (I think it's the DCT700). It only has a coax in, coax out, and RCA jacks out. If I connect the cable box directly to the TV using either output, it works fine. However, if I connect the cable box to the Tivo and the Tivo to the TV, the cable box's video signal doesn't seem to make it to the Tivo. I tried every combination of outputs from the cable box to the Tivo and the Tivo to the TV. The Tivo itself is fine as far a I can tell, I'm able to see the Tivo menus and got through the guided setup (had to skip the IR blaster setup for obvious reasons) and the shows she recorded previously in her old house play just fine.

I'd guess that the problelm is the cable box, since it's the only new piece of the puzzle, but I'm not sure that makes sense or not.

 

I did some more searching and found this thread.

Hopefully, the information in there will help.