I have following gadgets at home: Airtel HD-DVR, Samsung 40" LCD TV and Onkyo HTS-3300 5.1 Home theatre.
Video: Airtel HD-DVR HDMI Out to Samsung TV HDMI In
Select option of Stereo sound output over HDMI in Airtel HD-DVR
Audio: Airtel HD-DVR SPDIF Out to Onkyo AVR SPDIF In
Select option of Dolby Digital output over SPDIF in Airtel HD-DVR
Advantage: For normal channels i.e. one without DD 5.1, I do not switch on my AVR instead listen to the audio though TV speakers. (Its a greener solution too, saves electricity :c)
For HD channels with DD 5.1, I bring the TV volume to 0, switch on the AVR and enjoy the surround sound effects! (I am waiting for the world cup to begin
)
Note: If you want surround sound always on, then connect STB HDMI out to AVR HDMI in and AVR HDMI out to TV HDMI in (no need to use SPDIF). And select Dolby Digital or Dolby Digital Surround over HDMI in Airtel HD-DVR.
Earlier when I had Reliance SD STB, this was my connection:
Video: STB Component out goes to Component in of TV
Audio: Left and Right Audio out to Left and Right in of TV
No connection made to the AVR as no DD 5.1 out available from STB and I don't like the stereo to surround sound audio conversion.