For ATI video card link with HDMI to monitor or TV here's what you need
1) If you are using a DVI port you need ATI provided DVI-> HDMI converter to get an audio.
2) If you are using HDMI port then direct connection should work
3) Got to Control Panel, On Sound Option... Select "AMD HDMI Output" as the default Audio Playback... That should produce audio on your DLP TV.
I have 3 setups of HDMI to HDTV (70, 65, 52)... It should work