Red RCA input was faulty from the factory.

Here I must say that I had ordered a new adapter and here the red RCA input was faulty from the factory.
Had been looking for ever, until I came out that RED CINCH the adapter simply have to be broken. I just got on the White input sound via headset, when Red came no sound. Wired was all correct and right.

Today I got another new adapter and behold, both RCA inputs work directly.

So: If someone sometimes gets these problems: order a new adapter.

Greeting