AC3 -> SPDIF -> external Dolby Digital decoder

[DeSolo]

Sorry for my poor English - I'm from Poland.

The case is to send AC3 audio stream through SPDIF to the external DOLBY DIGITAL decoder !!!UNDER MS Windows 2000 Pro!!!

There is no problem in Win98SE.
Decoder recognize digital AC3 stream, and switch to Dolby Digital.

But the same stream under MS Windows 2000 Pro is not recognized as dolby digital signal, but sort of stereo Dolby Surround. Decoder stays in Dolby Prologic mode instead of automatic swithing to Dolby Digital.

Tip:
In iviaudio properties in Win98 SPDIF out is active, but in Win2000 is grayed in most apps, except the properties window in WinDVD. But under Win2000 even WinDVD will not send correct stream to ext. decoder.

My system is:
MS Windows 2000 Pro
SBLive 1024 (LiveWARE 3.0)
ServicePack 2
DirectX 8.0
registered iviaudio.ax (from WinDVD most up to date)
Wave Out: "Default WaveOut Device"

Please give me some advise.