This unit has a standby mode until a signal is applied. It then turns on. Speaker outputs from a stereo amplifier are applied to its inputs and room speakers are then fed from the cube's "speaker output" terminals. It also has a line input and can be driven directly from a CD player output or tape out of an amplifier. When any signal is applied the cube just begins to hum constantly. The output to the room speakers does not hum but there is no speaker output to the room speakers either. Cambridge Audio refuses to provide any service information on this unit. Does anyone have any experience with these? Thanks, Lenny.