This product was introduced in the early days of CD players when most people would have had an amp with either a spare AUX input or Tuner input but no dedicated CD input. Because the AUX or Tuner input would usually have an input sensitivity of a few hundred mV and the output of most CD players was of the order of 2 v or more the switching unit attenuated the CD output by 6 dB (or half) so that switching between CD and Tuner would not result in a large jump in volume and the risk of input overload was removed. This is what the network of resistors is, a simple potential divider (like a fixed volume control).

Attached is a pdf of the original instruction card from that time.