Good evening Christian,
Do you get audible sound after disabling the FxSound Speakers (normally set as Default Device) in Windows Sound Settings?
Have you already tried connecting another device and/or using a different connection method?
Also, did you find the troubleshooting list at the top of the forum?
This is the only thread I found about S/PDIF a.k.a. the Sony/Phillips Digital Interface optical audio connection. This might be off-topic, because I’m not certain if this is related to your problem…
But the information does remind me of this bullet point in the list, which was information shared by our lead engineer:
There are 2 types of encodings, and 2 types of connections. PCM is what a CD player puts out, Dolby Digital is what a DVD player with a DVD movie puts out.
There are 2 types of digital connections: optical (called “Toslink”) and coaxial-digital. Both types of connections can carry PCM and DD signals.
SPDIF (Sony Phillips Digital Interface) is the specifications around which the digital connections are built.
(Copy-pasted from hometheaterforum.com)