However...
Even though a post is 'old'... a question unanswered can end up just 'clutter'.
In other words, other people may find these questions/posts later... so posting the answer here, is still useful. I agree with xs that an answer directing people to search elsewhere... isn't much of an answer. Since xs didn't come back to it... maybe I will... (or not

).
What I am looking for is how much value there is in, and what you need to make use of, 6 channel sound... to determine whether I should keep it.
I would suppose, that if you don't have a 6 channel speaker system, then keeping the 6 channel sound, and deselecting the 2 channel output, is going to result in the lesser quality (as in the downgrade in vocals that CJ experienced)... just guessing. "Comments" are often in yet another 2-channel audio stream.
I do notice that some DVD player -software- (like older WinMediaPlayer versions) just don't have the same volume output, and you end up having to crank up in-program volume and regular volume control, just to hear decently... whereas other software, like
PowerDVD, seems to have more 'normal' playback volume.
Otherwise, on some DVD's you have fullscreen and wide-screen selections... two complete copies of the content... so you can choose to eliminate one of those and keep all the audio streams... (but the 'comments'/audio may be tied to one version or the other, and not both full and wide screen?).
Anyway... maybe that helps a little.