Where can I get such a device (based on the description)?

I'm looking for a headset which allows me to play a ps4 sound or to connect a soundboard to what sounds I choose myself, then directly into the party chat and into my headphones for listening.

In plain text:

The headset needs an audio input that outputs the incoming audio signals via the microphone. In addition, I want to hear the incoming audio signals at the same time. My microphone should also be usable for my normal voice.

In theory, I need exactly this device: https://nyko.com/collections/playstation-4/products/sound-pad-for-playstation-4

But this is not sent to Germany but is only available in the USA… Does anyone know of an alternative

(I already have an audio interface: "Steinbeck Ur22mk2" which can't be connected to the ps4 if this is an answer)

You can do this via settings in some audio programs. And completely independent of the headset model or microphone.

What you linked there's not a headset that has completely different functions the part.

I know that this is not a headset, but it has exactly the function that I want, the whole thing only with the headset described is only a detour to achieve what the linked device can do, namely import pre-selected sounds into the ps4, which everyone in the party including me can hear as a user.

What exactly can I do with some audio programs? It's about the fact that I can do this on the ps4, or does it have a permanent effect like a root, which means that if I have changed my headset with a program, the settings are the same when I switch it to the ps4 pack?

I do not know what Ps4 is all capable of, but should be difficult to get that, I forgot the name for it but with Audacity so recording programs you can set something so that you can hear directly what you sing eg.