The connector in question is an 8-pin DIN in the back, which in the days of yore (almost eight years ago) would have been used for a CD changer. Since CDs are old news now, [Kalle] made use of ...

A CD-ROM drive that holds a small number of CD-ROMs for individual use on a desktop computer. Although it can swap discs, it typically contains only one drive and can only read one at a time.