Live TV & Radio without tone (1 Viewer)

[MirkoC]

TV-Server Version:
MediaPortal Version: mediaportal-svn-01-07-2009--22-21-Rev21306
MediaPortal Skin: blue3wide
Windows Version:
CPU Type:
HDD:
Memory:
Motherboard: Gigabyte GA-P35-S3G
Video Card: Terratec DVB-C Cinergy PCI
Video Card Driver:
Sound Card:
Sound Card AC3: Gigabyte GA-P35-S3G on Board
Sound Card Driver:
1. TV Card: Terratec DVB-C Cinergy PCI
1. TV Card Type:
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:
MPEG2 Audio Codec:
h.264 Video Codec:
Satelite/CableTV Provider:
HTPC Case:
Cooling:
Power Supply:
Remote:
TV:
TV - HTPC Connection:

Wihle showing live TV, or playing Radio, there is no sound output. The PC is connected via optical S/P-DIF to the amplifier. May somebody help me?