Spotify won't output sound on digital optical from Chromecast

[lucasiwa]

Plan

Premium

Country

 Germany

Device

Chinaphone Xiaomi

Chromecast (the normal one, not audio nor 4K)

Operating System

Windows 10 / android

My Question or Issue

Hi,

basically in order to use my beamer, playstation and listen to spotify, I have the following setup:

 Playstation, Chromecast and PC HDMI connected to an HDMI Switch/Hub, which in turn connect to an HDMI Splitter. The Video goes to the Beamer, the Audio through digital optical to the Soundsystem.

The Audio works 90% of the time with youtube, 75% with soundcloud, but there's little to no life coming out of spotify (sometimes it sound for around 2seconds). 

I tried to solve this issue by:

changing Chromecast  -> no difference, issues stays. The Chromecast works perfectly on TV

using Amazon Fire TV Stick -> works fine with Spotify and other services

changing cable -> no difference, same issue

using an analog output -> all apps, including Spotify,  work without issues

attach directly without HDMI Hub -> no changes

changing channels for audio output on sound system -> nay

changin output on splitter from 2.1, to 5.1 or "pass" -> no change whatsoever

Does it have anything to do with signal decoding? I have no idea what im talking about.

Help