Hello,
I had some feedbacks on the script_upmix :
first there was a mistake in method 3 ending in missing right
channel or left right inversion.
That is fixed.
Some think method 2 is quite "loud" : nice for music, concert,
musical video clip but less good for subtile dialogs and
atmosphere soundtracks.
It might be useful. Attached is newer version of the script_upmix
(bash script quite linux-universal)
Gérald