No offence to anyone but please research I said already.. I've studied all this in multimedia communication.
PCM is uncompressed audio provided by Tata sky.. D2h and others
Uncompressed means there is no audio processing by DTH operators.
While DOLBY DIGITAL is a lossless compression technology used to compress audio size to reduce bandwidth.
Since dolby is lossless it is adapted in various communication areas.
So the conclusion is PCM is equal or better than DOLBY DIGITAL
And D2h provides PCM 5.1 surround sound
Maybe this can help all of you
High-Def FAQ: Uncompressed vs. Lossless Audio | High-Def Digest