The legendary beolab 3500.
This 'Link' speaker is actually meant to be connected via a masterlink cable, the flat wide connector.
There is a possibility to program the beolab3500 to be used stand-alone with connection to the din.
Note, only one connection always works, either via masterlink, or via the MCL (din).
If you want to use the beolab3500 as a center speaker to a TV with headphone output a beolink converter 1611 is a solution, read this manual.