Apple Logic Express 9 - Manual (Page 293)

Choose Window > Environment (or use the Open Environment key command, default
assignment: Command-8) to look at this object.
Another thing that happens in the background is the automatic creation of Mixer channel
strips for each of the multi-instrument sub-channels. Click the Mixer button at the bottom
of the Arrange window, and click the All button in the Mixer’s menu bar. You’ll see 16
channel strips, assigned to GM Device 1 to 16 (plus a couple of others for audio channel
strips).
293 Chapter 10 Working with Instruments and Effects