Video input on Motorola DCT6412 cable box?

On the front of the cable box there are the three easy to recognize yellow white and red input ports. I can't figure out how to switch the out put of the box to this input.

Long story: My computer is hooked up to my monitor directly with an HDMI cable. My cable box is also hooked up to my monitor with an HDMI cable. Both of these work perfectly fine and I merely need to press a button on the monitor and the display switches. The monitor has none of the previously mention video/audio input ports though. So I plugged the device I was wishing to hook up (Xbox 360) into the cable box. I cant however figure out how to switch what my cable box outputs from the TV to the Xbox 360. Anybody have any idea and/or am I missing something really stupid?