I'm just wondering if there is a reason its hidden in the floor? Or just for a cleaner look?
I've seen wifi extenders that plug into a wall plug and use existing wiring in the house to extend the range...but I think they need a ethernet connection to the router.
This is what seems the most confusing to me...first you say you have motorola modem/wifi with no router ports connected to dvr then you say you can connect to the cisco and dvr with ethernet so which is it?
Either way, port forwarding should not be an issue with the router. What you are going to do is run ethernet from the modem to "feed" the cisco 4200. At that point you can turn off the wifi signal on the modem (if it allows it) since it is buried and weak anyways. Then you will use one of the ports on the 4200 to connect ethernet to the DVR. The other open ports can be used for anything else that you can connect ethernet to that needs it, and if the wifi from the cisco isn't strong enough for your wifi needs over the whole home, you can look into an extender or repeater at that point.
The cisco should have plenty of options for port forwarding for your dvr setup, you will just need to figure out how to do it.
What cable service you have might make it easier to figure out how your motorola modem works. For instance I use xfinity with a router. I have all my xfinity wifi turned off, and just use my routers wifi. Same deal though...cable into modem, then modem feeds the router which supplys wifi and ethernet. I have one pc and one security camera setup plugged into ethernet and thats it, everything else is wifi.