Handbrake's downmuxed AC3's

[T0tum]

Iam doing backups in Handbrake (1st time), but due to my negligence i re encoded my sound instead of passthrough.
My TRUE-HD dolby 5.1ch using auto passthrough resulted in 640 Kbps 6ch AC3 and 4 times smaller than original.

So, considering there are several ways Handbrake can downmux AC3 audio, which one was used in my case?
If i were to keep this audio (very attractive due to its size) is this correct way of downmuxing the audio, or should i go with AAC instead?
Iam on 2.0 system now and cant hear the difference (do intend to keep surround), please advice.

[KarMa]

Well 5.1ch audio, is 6 channels. So you seem to of kept the same number of channels, and I can't see any reason why Handbrake would jumble up the channels randomly. Do you know what mixing setting you used?

[T0tum]

I have no idea what settings handbrake used, this is what i have in my log:

[05:16:45]  * audio track 1
[05:16:45]    + decoder: English (TrueHD) (5.1 ch) (track 4, id 0x721101)
[05:16:45]      + bitrate: 200 kbps, samplerate: 48000 Hz
[05:16:45]    + mixdown: 5.1 Channels
[05:16:45]    + encoder: AC3 (libavcodec)
[05:16:45]      + bitrate: 640 kbps, samplerate: 48000 Hz

It could be that handbrake extracted AC3 core from TRUE HD, like tsMuxer does. However i tested extracting AC3 core with tsMuxer and size differ a little.

EDIT:

Handbrake did re-encode my audio, because AC3 file sounds louder than AC3 core!
So, did handbrake use lossless TRUE HD to create AC3, or re-encoded already downsampled AC3 core? Not really sure which audio to keep.

[smitbret]

Why not just demux the audio track out of the BD with tsMuxer and then mux it back in to your file?