Well, I didn’t. I happened to be driving the M:C with an iPad, recorded what I was doing using AudioShare, and then tried to see how to play it back on the iPad. To my astonishment, I could hear it, even though my headphones were still plugged into the M:C. This information is buried in section 12.4.6 of the manual, which talks about controlling the input gain, and says that the signal goes to headphones and analog out.
Just posting for the benefit of those as clueless as I am.
