Q: I'd like to extend my wired network using Airport Extreme

Right now I use a Time Capsule as my main router and also for backup, which it does exceptionally well. I wish it had more LAN ports, though! Here's the situation: I have the Time Capsule set up in my TV stand, because that's where my cable modem is, and most of the devices that are connected to my network (TV, Apple TV) I also have a cable that connects to my iMac, which is upstairs. I would like to buy a new Airport Extreme to take advantage of the dual band feature for faster connection of my iPad, so I'm thinking of making the new Airport my new main router and then move the Time Capsule upstairs and use it to extend the network (wired, not wireless) to my iMac and any other devices I want to connect to it upstairs. How should I go about doing this, and is there a better way? The main thing is that I want to maintain wired connections for certain devices (Apple TV, TV, and iMac). Thanks.