I believe the issue is that your receiver doesn't support the newer AAC 5.1 format of your downloaded MP4s. The best you can do generally will be Pro Logic equivalent sound. More related info here:
Sharp LCD Tv with 2 HDMI Inputs, 1 optical out
HP Laptop Pavilion with HDMI output + NVIDIA CARD, Windows 7, Windows Media Player, VLC media player , Media player Codec Pack (downloaded from CNET)
Bose 5.1 speaker system
Denon AV Receiver 2801 with Dolby & DTS,does not have HDMI support.
Connections: laptop to TV with HDMI and TV to AVR with optical cable.
Settings on AVR are on digital input with output selection for automatic Dolby Digital/DTS/Dolby prologic.
Watching MP4 files with AAC 5.1 downloaded from from various torrent sites from reputed publishers like SecretMyth etc.
Problem is when watching these movies the AVR display panel shows the sound as in Pro logic mode and the sound quality is not as good as in DD or DTS.
Whereas whie watching some other movies, torrents(seldom available) having info saying that audio is in Dolby Digital, The AVR panel this time shows DD and the sound quality is perfect.
Question is how to watch these AAC 5.1 movies with similar quality of sound as in Dolby Digital/DTS?