Hi Prasanna
Even I got Airtel HD DTH when I purchased my LG 50 inch plasma last week. I live in Madipakkam. Not sure about the answer to your question (hopefully others would barge in to help you on that), but can you check if you are getting 5.1 sound from your HD box in the Nat Geo HD channel? I tried connecting the Coaxial Digital Out of the HD box to the Coaxial In of my Yamaha RX-V459 AVR and it's showing only stereo. I get nice 5.1 DTS and Dolby Digital sound when I use the same cable to connect my DVD player.
I have already escalated this to the Airtel Nodal Officer, since I feel this is cheating as Airtel keeps advertising "7.1 Dolby Digital Plus Surround Sound" in all their newspaper and TV ads for the HD DTH.
Please do check on the same and let me know.
Warm regards,
Venkat