You can't turn off the Z-5500 using the Soundtouch Control Center, but you can use the button to put it into Headphone Mode. This mode enables you to listen to your headphones while dimming the backlit LCD on the SoundTouch Control Center.

To control the system power, you'll need to use the switch on the rear panel of the subwoofer.

NOTE: In the product documentation, all references to the System Power function on the Remote Control and SoundTouch Control Center should read: "Headphone Mode."