ASUS P5W DH & DTS output

[gusangora]

I have the ASUS P5W DH Deluxe, which has onboard Realtek HD Audio and Dolby Digital Live 5.1
I am using the nvidia purevideo video and audio codecs, with audio set to output via S/PDIF to receiver.
When I play a movie with a DTS soundtrack, the HTPC is outputting Dolby Digital to the receiver, not DTS.
When I test the audio output via the Control Panel, the test DTS sound is displayed as DTS by the receiver.
So why is MediaPortal not outputting DTS?
Where is this conversion occurring?
Any help will be much appreciated.

MediaPortal Version: 0.2.2
MediaPortal Skin: Blue2wide
Windows Version: Vista Home Premium 32 bit
CPU Type: Intel Core2 Duo 2.4 E6600
HDD: Seagate 320g SATA2
Memory: 2g Kingston DDR2 800
Motherboard: ASUS P5W DH Deluxe
Motherboard Chipset:
Motherboard Bios:
Video Card: XFX nvidia 7950GT
Video Card Driver: nvidia beta 100
Sound Card: Realtek HD Audio
Sound Card AC3:
Sound Card Driver:
1. TV Card: DNTV Live
1. TV Card Type: DVB-T
1. TV Card Driver:
2. TV Card:
2. TV Card Type:
2. TV Card Driver:
3. TV Card:
3. TV Card Type:
3. TV Card Driver:
4. TV Card:
4. TV Card Type:
4. TV Card Driver:
MPEG2 Video Codec: nvidia purevideo
MPEG2 Audio Codec: nvidia purevideo
Satelite/CableTV Provider:
HTPC Case: Silverstone LC20M-B
Cooling:
Power Supply: Enermax Liberty 620W
Remote:
TV: Sony SXRD KS70R200
TV - HTPC Connection: DVI=>HDMI