So I encode and transcode media to MP4 containers intended for use on my ATV2 and my DD 5.1 surround system. My audio system reports the audio streams that it's receiving as PCM using Dolby Pro Logic II. I understand that the ATV2 can send a Dolby Digital signal to the receiver but it depends on how the audio stream in the file is encoded. Today I somehow transcoded a documentary that had the standard AC-3 audio stream that I then converted to an AAC 5.1 format. This file is different though, it has somehow engaged the Dolby Digital on my receiver and sounds noticeably better than my other audio files. Does anyone know what I did right this time?