I found one possible answer...
Why does it have no audio when I watch TV?
1. Please confirm IRQ is works properly.
2. Make sure to connect a line between Combo card "audio out" and Sound card "line in". And connect your speaker to Sound card "line out".
3. Please enable "line in" of speaker properties (record & advance option) in task bar.
You may find further assistance here
http://www.prolink-usa.com/english/faq/playtv/playtvfaq.html#Q1-4: