7.1 and DVD inputs NEED ADVICE

I'm using my 990's 7.1 inputs from a Panasonic DMP-BD55 Bluray player. I also have the Bluray player connected via optical (assigned to DVD) so when watching standard DVD I can use the 990's decoding instead of the players. I have noticed something weird at times and I was wondering if anyone has had the same issue or has any advice. There are times when watching standard DVD via optical when I notice the front screen of the 990 displaying Dolby Digital and Pro Logic II. When displayed like this the sound is great. It has great low end extension and full bodied. Other times I see simply Dolby Digital displayed and the sound is very thin and is lacking most of the low end extension. I also notice this at times when watching HD cable which is connected to Video 1 via a coax digital cable. Any help would be greatly appreciated. Thanks.

As I understand it, when the screen says only Dolby Digital , the 990 is simlpy decoding the information from the DVD. When it says Pro logic II, it is processing the signal to matrix out the various channels. You can always get to Pro Logic II by toggeling the Dolby Modes button on the 990 remote.

That's pretty much it. Dolby Digital will record the sound on discrete tracks. For example 5.1 sound is recorded on 6 tracks. You can also record the 5.1 sound on as few as 2 tracks which is called matrixing. The Pro Logic II will decode these matrix channels and output the 5.1 (6 channel) sound. Pro Logic II can also take in stereo sound and process it up to 5.1 output. I believe the 990 will select the decoder based on the format recorded on the disk.

KOYAAN, I've tried to scroll through the different Dolby modes to find Dolby Digital II with the remote as well as the surround mode button on the front panel. When it's reading Dolby Digital and I scroll it only gives me one other choice. The other choice displayed is Dolby Digital + Dolby VS 5-SP WIDE. This happens when I'm using a standard DVD or watching digital cable. I would prefer not to use any other processing but the standard Dolby Digital sounds very thin. What would cause this?