What source would result in best AAC down mix?

[DataMeister]

If I have a Blu-ray with DTS-HD or TrueHD and want to down mix to a stereo Dolby Pro Logic track, what is going to give me the best quality?

Would it be starting with the uncompressed HD track or just using the lossy 5.1 track?

I'm not sure how the down mixer is working. Would having a 7.1 track add extra noise, or is it throwing out extra channels it doesn't need? Is it also down sampling from 24/96 to 16/48 or something similar or does the AAC keep the same bit and sample rates?

[Lostless]

As far as an input, both DTS-HD and TrueHD are virtually identical as far as audio quality. And encode as 256Kbs or higher to retain as much audio quality.
As far as the down mixing to stereo, I use just stereo. It won’t erase any of the tracks, but mix them to left and right. For a while there there were bugs in the prologic encoder that put sounds in the wrong place. Not sure if it’s been fixed. Give it a try and see what you get.

[Lostless]

To continue, I think handbrake downmixes to 48khz. The 16/24 bit is irrelevant because you are using a lossy codec (AAC)

[Deleted User 11865]

Definitely use the lossless track as a source.