Hows the digital box connected to your TV? If it's using HDMI or some other input other then the TV's analog tuner, the TV's analog tuner will be unused and you can always always use it for the cameras. This is what i do.. I have 6 cameras and I have each one of them is on it's own analog channel.
I have 6 modulators that are mixed together... channel 14, 44, 48, 60, 64, 68
I then take that mixed output and run it into a splitter and send this feed to all the TV's in my home. It's like a mini cable TV system. We only use the TV's analog tuners to view the cameras.