Optical audio out problem (MacMini Server 2012)

[barracuda156]

For some reason I cannot make optical audio out work. MacMini 2012 with Catalina (I also have 10.6.8 on it, and it doesn’t work there either).
Any idea what may be the cause?

Identical audio setup works with my MacBook Pro (so cables and audio devices are not to blame).

 

[IngoX]

Maybe dust in the audiojack?
In Sound preferences, does it switch to digital out when you insert the toslink plug?
See any red light out of the cable?