Hello,
@Reiner: Did you modify the 737NGX_Options.ini (your FS folder / PMDG / PMDG 737NGX / ). You have to add following lines:
[sDK]
EnableDataBroadcast=1
Then you can use external hardware with the PMDG - at least theoretical.
@Nico: I've sent you a PM. Maybe you can check it? Thanks!
Alex