Looking at the signal levels my gut is telling me is something to do with OTA or tv signal interfering with the DOCSIS signal that the modem uses. My guess is you're looking to either remove, replace upgrade or bypass some kind of signal amplifier that's used in your apartment complex to spread the signal to the different apartments. If so, the easiest route might be just to ask Cox to get your own line installed to your apartment so it doesn't even touch that amp and they don't have to replace or change anything that affects everyone.