I can't send 5.1 sound using SPDIF

The only app that can send dolby digital 5.1 throw SPDIF is the PowerDVD 4.0 what came with my laptop

IF I try another DVD software or another version of PowerDVD, the SPDIF sounds only stereo

My sound card is a realtek AC97, but PowerDVD 4.0 say:
Multispeakers Audio Device : Sonix USB (not in use)
SPDIF Output Device : Sonix USB (in use)

If I try A newest verion of PowerDVD say:
Multispeakers Audio Device : Realtek AC97 (not in use)
SPDIF Output Device : Not Detected

WHY????

any idea?

I would like to use 5.1 SPDIF with other software like windows media player clasic, games, etc...

PD: I try to modify AC3Filter settings but it doesn't work