DirectShowMBS AMCrossbar

Hi, I’m back to getting my hands on DirectShow MBS. I need to work with analog cameras and I have to set whether to take S-Video or composite signal. Should I make use of the AMCrossbar class?
I saw the PlayCap example - I try to recall

Dim AMCrossbar As DirectShowAMCrossbarMBS = srcfilter.AMCrossbar
If AMCrossbar <> Nil Then
  MsgBox "Result: "+Str(AMCrossbar.Lasterror)+": "+AMCrossbar.LasterrorMessage
  MsgBox "No AMCrossbar."
End If

but I get “No AMCrossbar”.
I have very confused ideas not only on HOW to implement the solution, but on WHAT I should do.

Any help?