Set volume for optical audio output.

[Guest]

Hello, how can I set the volume level for the optical output?
If I change the volume, the actual volume doesn't change until 0 when it becomes mute.
The only thing I can change is the volume related to the application but I want to set the general volume controller, not the application-specific.
As long as I experienced KDE distros (openSUSE and Kubuntu derivatives (Mint KDE and Netrunner)), everyone had the same problem. Only with Mint with Cinnamon I was able to set this specific volume. But I prefer KDE for many reasons.
Any help will be appreciated.

[Teunis]

A lat suggestion but maybe you're still checking this thread.

Have you tried to play with the pulse audio controller or pavucontrol?
An alternative might be Veromix.

These give more and often better options for controlling various non-standard channels.