I hear the wireless boxes might work if you use ethernet to connect it to your own router. Can't make any promises but it's worth a try. The other option would be to switch to a coaxial based Contour box but if you could run coaxial to that room you could probably run ethernet.
Have you considered dropping Cox TV and going with Youtube TV with Chromecasts? That way you can make all your TV connections wireless or wired(they sell a power supply with a ethernet adapter) depending on what you have. It's 73$ a month which I think is less then what Cox charges if you take into account box rentals(10$?). You would also save on the cost of the Panoramic gateway.(14$?)
What are the reasons you wanted your own modem and router? If because of weak wifi signal, you could buy a Access point(AP) and run ethernet or MoCA to where there is weak signal and install the AP there.
