I'm pretty sure there's only 1 controller. The other thing that looks close to it is a slave. They have similar recipes, but I believe the controller uses diamonds and the slave uses gold. I might be a bit off...
Anyway, I don't think it can just touch on the corners. It needs to touch on the sides, and you can use frames to connect them as well. But, that's all there is to it. As long as it connects directly to the controller and there are slots open, it should work. I've been working with this myself for the last few weeks (before taking my brief DOOM intermission) and that's literally all there is to it. I have a whole 25x16 room lined with drawers with a single drawer controller in the center, connected to the walls via oak frames under the carpets.
sometimes the items can take a few minutes to find their destination, I've noticed. So if you gave up early, check it again. That happened to me my first time through. I thought it was broken, but it just took a few minutes to update.