Modem and Wi Fi

To get a second modem to work, you would need to pay for secondary internet service on your bill.  But you could set up a router as a AP or repeater. MoCA might even work if you have a cable outlet in the room. But these wouldn't be anything Cox can help. I can give suggestions if you had a price point in mind.

You can add a wireless router as an access point to extend your existing WiFi network. See this for help doing that...

http://www.dslreports.com/faq/11233

Another solution, and one that I use for my wife's desktop PC, is a pair of power line adapters. These are the ones I bought a couple of years ago.

http://www.amazon.com/ZyXEL-PLA4205kit-HomePlug-Powerline-Wall-plug/dp/B005GCSZD6/ref=sr_1_3?s=electronics&ie=UTF8&qid=1416792506&sr=1-3&keywords=zyxel+powerline+av+500+mbps

Using powerline adapters you can also extend your wireless network by adding either another router, see above, or a wireless access point in a different part of the house.

I don't; think you can connect a second modem to you one line,but they do sell signal boosters on amazon and best buy to boost your in home signal