You can only remove the network tuner channels once you've gone through setup. If you haven't gone through setup, you will occasionally be prompted to do so. So you can do the setup and then go into customize channels and just uncheck the entire source.

Btw, just in case you are not aware, you can use the DVR in Live Channels for free if you use the network tuner as the source. You may already know this and not want to for whatever reason but just letting you know that since a lot of us consider that a big plus of using Live Channels.

I don't know how the DVR does or doesn't work with cable channels. I only have experience with OTA channels.