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When compare AAC and AC3, both having 6 channels (5.1), it all depends on what bitrate is used in both formats. Because AAC is more advanced lossy audio format than AC3, it will produce better audio quality than AC3 with same bitrate, especialy on low bitrates. At the same time can't compare low bitrate ACC agains high bitrate AC3. AC3 will produce higher quality audio in that case.
Dolby Pro Logic II is not an audio commpression format, unlike AAC, AC3, and DTS. It is decoding technology that processes any high quality stereo signal source into 5.1 and simulates 5.1 channel surround sound.