No audio output from optical (stereo)

I’m having a somewhat weird problem with my WD TV. Normally the WD is connected to my TV with a 2m HDMI cable, it’s also connected to an external D/A converter using optical out (set to stereo). With this setup everything works. If I then connect the WD to my projector, using a 10m HDMI cable, then the optical audio out stops working.

Does anyone here have any kind of explanation to why optical out stops working with a longer HDMI cable attached? I’m using a PS Audio DAC, so unfortunately i can’t use any of the other sound ouput options.

from my own experience, I notice that after using a HDMI cable around 3 to 5 meters, the media player will start loosing video and sound… so might be the cable.

if you tried testing the unit with that cable on a TV?

It hasn’t been tested on the TV yet as the cable is installed in a way that makes it difficult to remove. I’m using a double shielded HDMI cable, the picture quality on a 160" screen is spotless with the 10 meter cable. Even if there is some inteference, it still doesn’t make sense to me that the optical output should shut itself down.