I have an IR eye without labelled buttons, just like yours.  It also does not have the auto-contrast, so I expect it's the same model, and as far as I can see, it's no different to my other IR eyes that do have labelled buttons, and it works just the same as those. I don't have a Beosystem 4 but when connected to my Beolink Passive amplifier, the buttons work - Timer (top), Volume (middle rocker) and Play (bottom).  I've also tried it connected to a Beolink Active, and it worked just the same. Are the two LEDs illuminating on your IR Eye, and do they toggle on/off when you press the Timer or Play buttons?  If they don't come on at all I would suspect a problem with the IR eye or it's wiring - the wires do easily come loose inside (that's happened to me more than once).  

The Beosystem 4 only have the connection for the IR signal, so it can not use the functions from the buttons even though they are there

I did not know that!  That does explain however why they released a version that had no labels on the buttons.  I always wondered why.