Checking a 5.1 M4A file created by QAAC using MediaInfo, you may notice a certain difference between two distinct values related to the "channel count". I would assume that MediaInfo just reports header values as they are found (is there another AAC / M4A analysis tool to compare?).
Is this a "bug" of QAAC (putting a wrong value in a header field), or based on a peculiarity of the AAC format (e.g. multichannel encoding being an extension to stereo since MPEG-2 BC audio)? ... Well, I may be wrong here, AAC is also known as MPEG-2 NBC (non backward compatible), so I hope there was no similar mistake.
General
Complete name : ToS_QAAC.m4a
Format : MPEG-4
Format profile : Apple audio with iTunes info
Codec ID : M4A
File size : 37.4 MiB
Duration : 12mn 14s
Overall bit rate mode : Variable
Overall bit rate : 427 Kbps
Encoded date : UTC 2014-06-04 06:30:09
Tagged date : UTC 2014-06-04 06:31:16
Writing application : qaac 2.38, CoreAudioToolbox 7.9.8.3, AAC-LC Encoder, TVBR q91, Quality 96
Audio
ID : 1
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 12mn 14s
Bit rate mode : Variable
Bit rate : 426 Kbps
Maximum bit rate : 578 Kbps
Channel count : 2 channels
Original Channel count : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Compression mode : Lossy
Stream size : 37.3 MiB (100%)
Encoded date : UTC 2014-06-04 06:30:09
Tagged date : UTC 2014-06-04 06:31:16