That raises an interesting business question. Many software packages have a regular and a Pro version, presumably because they think some people will not buy at the Pro level price. Once people buy the regular version, some will update to the Pro version. So, would a Lite or Audio only version attract customers who would not buy at the full price? Or would it simply mean people who were going to buy now would opt for the lower price and cannibalize revenue?
Adobe Photoshop is an example - Elements is Photo only and Premiere adds video editing.
Jim has probably already worked through this, but it is food for thought.