Unfortunately I can only confirm this. I have been using various input methods, but most of all I would like to be using my Apogee Duet as an instrument input. The menu "File -> Audio Input -> Duet USB" in "LS Tune" is shown as it should, i.e. "LS Tune" obviously sees the various input devices on my system. However choosing that menu does not place a checkmark beside the menu command as I expected and worse, it does not connect to that input for receiving the wanted input signal. I tried other input sources (built in etc.), but all to no avail, "LS Tune" seems never to "hear" anything. Verdict: On a Mac the application seems not able to receive any input signal.

This is all that I can report at the moment.

OS X 10.9.5 (Mavericks), well maintained system.