This isn't complete at all.
Check your software from your system. Update it to at least 15.2. (not possible with system2 mk1)
Assign in the servicemenu under "plasmaversion setup" the slot 2 to decoder or AV as Y/Pb/Pr (2 different settings to make)
Then choose at the setup under AV or Decoder for STB(DTV)-Y/Pb/Pr or STB(Vaux)-Y/Pb/Pr.
This way, when choosing DTV or Vaux, the system 2 switches the panel to use slot 2 as videosource.
More options possible but for now something to experiment.