@Tantor ok you want to capture the audio output of the CD-player for CamillaDSP processing with the following chain?:
CD Player ---- [toslink/spdif] ---> toslink/spdif convertor to usb ----- [USB] ---> Raspberry Pi
Probally your USB toslink/spdif convertor will appear as an an audio capture device with in the Raspberry Pi OS.
You can instruct moOde to use it as an audio source with a special playlist in moOde.
The article moOde with USB input will point you in the good direction.
CD Player ---- [toslink/spdif] ---> toslink/spdif convertor to usb ----- [USB] ---> Raspberry Pi
Probally your USB toslink/spdif convertor will appear as an an audio capture device with in the Raspberry Pi OS.
You can instruct moOde to use it as an audio source with a special playlist in moOde.
The article moOde with USB input will point you in the good direction.