Panasonic SC-PT660 digital in doesn't work

Select to suit the type of audio from the OPTICAL IN terminal on the main unit.
1 While in “D-IN” mode
Press and hold [—SETUP] to select “MAIN/SAP”, “DRC” or
“PCM FIX”.
2 While the selected mode is displayed
Press [up, down] to make the setting.
MAIN/SAP mode (Only works with Dolby Dual Mono)
MAIN, SAP§, MAIN+SAP§ (stereo audio)
§ “SAP” = Secondary Audio Program
Dynamic Range Compression
DRC ON: Adjust for clarity even when the volume is low by compressing
the range of the lowest sound level and the highest sound level.
Convenient for late night viewing. (Only works with Dolby
Digital)
DRC OFF
PCM FIX mode
PCM ON: Select when receiving only PCM signals.
PCM OFF: Select when receiving Dolby Digital and PCM signals.
[Note]
Audio that is input through the OPTICAL IN terminal cannot be output
through the HDMI terminal.