Welcome to the forum, Greg and Nicole!
When I was younger, I used to use speaker wires with RCA connectors, and I used RCA extension cables to make them longer. Worked just fine. You could always give it a try and see if you notice a difference in the sound (connect the speakers up before you place them too far away to use the included cables, and swap the extension cables in and out and check if you can hear a difference). You won't need barrel couplers (unless you already own some) because you can buy RCA cables with a female jack on one end and a male jack on the other.
Also, like Alex said, you can extend the wire on the other end, too. You'd just buy some speaker wire, connect the two wires together, and wrap them to prevent shorts. You can solder them, twist them together, use wire nuts...anything that gets good contact between the cables.