Where to plug in the jack on a PC

Hi,
You say that the black jack socket is at the top of the tower. In the front? It must be a headphone output, because if your PC is equipped with analog outputs for 5.1/7.1, the outputs in question should be in the same place as the green output on the motherboard.

So if it is indeed a headphone jack, you actually have the choice between this one and the green output at the back, which is a line output. Both outputs work the same way; one is designed for headphones while the other is more for multiple uses, such as being connected to an amplifier or a mixing desk, for example... whether you use one or the other doesn't change anything in practice, even if a line output is not electrically equivalent to a headphone output. If the black jack is indeed at the front of the case, it's mainly a matter of ergonomics: are you going to need to unplug your audio system?
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It’s not because it’s difficult that we don’t dare; it’s because we don’t dare that everything becomes difficult (Seneca)