I did not include more information because I hoped that I simply missed something that should be clear. My technical knowledge in this subject is quiet rudimentary.
I use the Generic X86-64 Windows LE on a very old desktop with integrated gpu. I will check via SSH next week whether there is CEC-compatibility or not and if so, I will try a newer cable with CEC-support. I have no pulse-eight-adapter and think I won't buy one, because it is more expensive than my whole setup.
If I find something working, I will post it here. Until then I thak you for your support and insights!