Not sure if this helps or not, but many higher end surround sound receivers will do this for you already. They will sense which input is active and select this as the source signal to amplify. Generally what they do is select the highest quality signal available for a given type of device and use that input. You can use this feature to "trick" the receiver into auto selelcting a source for you.
For example : the DVD is connected to use the descrete 6 channel input & component video output, and the satellite box is connected to the 2 channel input & the TV's video input. The 6 channel input is considered the better signal over the 2 channel, so when the DVD player is on, the receiver will choose that audio input and also select the corresponding video connection. When the sattelite box is on the 2 channel audio input will be selected with its video connections. The receiver is left set to video input.
I have done this before when there were not enough separate inputs for all of the video sources, but there were different "types" of inputs/outputs for the same video sources. You can still manually select input / output combinations via the receivers controls, but the auto select feature will handle everyday combinations.