The answer is a Harmony. Hit the watch Cable TV button and the TV, cable box, and receiver turn on and the input changes to the cable box.
Want to watch a DVD - hit the Watch DVD button and it turns off the cable box, turns on the DVD player, switches the source on the receiver to DVD and changes the remote's controls to mimic your DVD player's remote. Harmonys are super simple. One remote really does replace the whole collection.
But if that isn't workable you might look at splitter on monoprice.com.