I do not know which line precisely. I trusted the user from the xda thread, who said their edits in the mixer_paths_0 file fixed the issue. I copied the three file parts the user posted, merged them into a single file, which I then placed in the previously mentioned directory.
In order to find which values differ between the original and edited mixer_paths_0.xml files, I used the diff command (with the -w option to ignore possible blank spaces differences) in Linux terminal : diff -w mixer_paths_0original mixer_paths_0edited.
A file containing the output of the diff -w command can be found here. In this file, first which lines differ is mentioned, then the values of the original file are shown, then, after a - - - separation, the edited values are displayed.
The result is that there are many edits, so I cannot really tell you which one is crucial. The file I linked showing the differences should be a good place to start I guess.
Maybe someone who knows more about this could help us pinpoint which line is important to fix the echo problem ?