After receiving some questions via PM decided to put here a part of an mail that I've received from Julian Fischer:

"... With the switch you can activate or deactivate the optical input in the same sound setup. This is used when you have connected the CD drive via the optical input and the radio via analog input. For the C-DSP this feature is not so important because the A/D and D/A converters are really good, so that there is no big difference between the optical and analog input but for the P-DSP this feature is more noticeable.

Regarding the connection you are right, the switch switches between ground and +3,3V because we need defined values at the controllers input. Just do nothing might cause an undefined state which is not so good. ..."

As I received this message already after my remote controller was made and installed on 4 Wire cable I could not really test this (switch) feature.

The only thing I noticed in comparision to informations found on forum is that I DIDN'T notice any wierd/strange/dangerous noises when I was switching the input sources with my laptop when my system was ON with the amps connected and running.