The amplifier mode button places the amplifier into one of three difference configurations. These configurations will be applied when you click the apply button. Applying these settings will also result in the crossover settings being cleared out as a result of the changes in the way the filters are applied in the different modes. All of the processing panels will close as well.
This mode is the default configuration for the amplifier. In this configuration the amplifier will act as a typical amplifier. It can also be referred to as 2 x 2 mode. Each channel acts independently.
This mode is typical bridge mono mode as the amplifier will act as one large single channel amplifier. The output wiring must be changed to match this mode. With the USP4 module installed in a 2 Channel CTs amplifier, this control still functions. It is not necessary to move the switch on the rear of the amplifier. The light on the front of the CTs will not illuminate indicating it is in bridge mode however.
This mode is a different mode than “Y”ing the input signal. It is designed to make it easier to use the crossover in a 1 x 2 mode. In this mode the processing blocks before the crossover are all linked together and only one input processing chain is shown. This will allow you to treat the amplifier as a more conventional 1 x 2 crossover. If you want to send the same signal to both channels but not process it the same that can be done through the source routing processing block.
If you are connected to the Internet you can find a video overview of this feature at:
http://www.crownaudio.com/tutorials/