The cable box will take the digital channels and down convert them to analog for display on a TV; meaning that unlike your incoming cable signal, the RF output on your cable box only contains analog. The HDHomeRun is a digital tuner, there's no analog to digital conversion involved.
What this means is that while the HDHomeRun cannot be connected to the cable box, it can take the position of the cable box, providing the ability to tune unencrypted digital channels directly, with no loss of quality.
