So today I finally got around to enabling the auxiliary input for the stereo in my car. I was over using the radio-transmitting device because of the poor audio quality.
The Blaupunkt 2620 head unit that came with my 04 Vectra supports AUX, but doesn’t have it enabled from the factory. And there is not a lot of information online regarding this system. So I’ve recorded the details of what I did here.