I'll be anxious to hear the answer to this as well.
When they first installed this new "panoramic" modem'/router, they also left my old apple airport extreme in place so I would have another network choice. The five year old airport had significantly stronger signal and faster speeds than the new panoramic modem/router. The only way to get internet upstairs, however, was to charge me another 5 dollars a month (on top of the 10 I was already being charged for this weak modem/router) to install an extender upstairs. Of course, they had to put a splitter on my TV cable in order to do that, so now I have a degraded, digitized, choppy TV signal because a splitter will degrade the signal even if there's nothing attached to the second outlet. I tried explaining that to my tech, but he clearly knew very little about signal or even internet.
Upshot, don't get it, people. Bring in an outside tech expert. They can help you extend your signal without a monthly rental for substandard equipment. They may be more expensive than the $70 cox will charge you for a visit from their "expert," but it will be a 1 time fee and you can be sure you'll actually have good internet.