To select unity gain, first switch the NAIT 5i into program mode as described in Paragraph 20.2. The AV input button will illuminate if unity gain is already enabled. If it is not enabled it can be activated by pressing the handset 4 key or front panel AV button. Deselect unity gain by again pressing the handset 4 key or the AV button. Unity gain only becomes operational or is cancelled on exiting from program mode by pressing and holding the handset prog key or front panel cd button.
Note:
The unity gain feature must be used with care. It effectively by-passes the NAIT 5i volume control leaving any signal connected to the unity gain input to be passed to the power amplifier and speakers at full volume. Additionally, if an input is selected which has unity gain enabled, the volume handset functions will be disabled and their indicators will turn off. This will be flagged by the volume indicator flashing if its handset keys are used
If the remote prog button and the front panel buttons work, then you should be able to activate deactivate av unity gain, according to those instructions.
That is telling you that the amp is in program mode.
If you press the av button when in program mode, does it alternate between on and off? If it’s on, then av bypass is on.