Can someone confirm that the sound from my DVR box via Optical Link to my home theater is indeed Dolby 5.1?
Yes and no. It depends on the encoding from the program source. There are many channels that only encode at 2.0. Try HDNET or HDNET Movies - I believe they are always 5.1. Also, some channels will send 5.1 encoding but only have 2.0 or 1.0 actual audio.
A lot of the local HD channels will only be 5.1 during prime time network.