Your receiver probably shouldn't fall back to Dolby Pro Logic (a two-channel analog to four-channel surround process). It should still be Dolby Digital, just two channels.
I suppose you could try to apply Pro Logic to the audio, but I would guess that anything done outside the late eighties and early nineties it wasn't expressly encoded for it.
Not really. Nothing has to be expressly encoded for Dolby Pro-Logic anymore, as there is more than one type of Dolby Pro-Logic.
The original takes a 2 channel PCM stream and creates 4 distinct channels Left, Center, Right, and Rear.
Dolby Pro-Logic II can take any 2 channel audio and create 5.1 surround sound.
Dolby Pro-Logic IIx can take any 2 channel audio (or dolby digital 5.1) and creat 6.1 or 7.1 surround sound.
Dolby Pro-Logic IIz can take any 2 channel audio (or dolby digital 5.1, 6.1 or 7.1) and create 9.1 surround sound.
I'm sure he is talking about using one of these newer versions of Pro-Logic and just calling it by the generic name.
As the others have said he should set his DirecTV receiver to have Dolby Digital on. His receiver should be set to use Dolby Digital whenever it receives that format, and use the most advanced form of Pro-Logic available whenever it recieves a 2.0 format (indluding DD 2.0).
The problem he may run into every now and then is channels/programs that don't format their audio correctly. Every now and then you will run across something that has the audio mixed as DD 5.1 but all of the channels except the front left and front right channels are empty. This should have been send out as 2 channel PCM or DD 2.0 but someone screwed up. When this happens there really isn't a whole lot you can do about it, because as far as the DirecTV receiver, and the AV receiver are concerned it is a 5.1 signal so it won't try to do any processing on it. The only thing you can do if this happens is turn off Dolby Digital on your DirecTV receiver until that program is over (assuming it is something you want to watch with surround). That way the AV receiver will just get a 2 channel PCM signal which it can then use Dolby Pro Logic to create surround sound from.
Edited by Beerstalker, 20 February 2014 - 01:15 PM.
Sometimes when I reflect back on all the beer I drink I feel ashamed. Then I look into the glass and think about the workers in the brewery and all of their hopes and dreams. If I didn’t drink this beer, they might be out of work and their dreams would be shattered. Then I say to myself, "It is better that I drink this beer and let their dreams come true than be selfish and worry about my liver."
-by Jack Handy