I have finally had time to look at Yanko´s blog in more detail. In a recent post, he makes a persuasive case for the Revolution featuring microphone input.
In a number of patents, he has come across an audio input other than the game disc. He has cleverly illustrated this by colouring in the various parts of the patents´ diagrams. The conventional input is shown as red, the additional input as blue.
He then comes to the conclusion that the only feasible answer is that the additional audio input must be a microphone peripheral of sorts. Please have a look at his article. Source / Image source: Yanko´s blog