Hello!
I found outdated info on this page: http://musescore.org/handbook/play-mode
Look at the last heading "Sound in Ubuntu" wich points to Installation page to "Linux" heading, wich was totally reworked and info about setting sound in Ubuntu was deleted.
And I have aint found it anywhere in handbook, as I understand this is not needed anymore, so, could you please remove this heading or point users to Ubuntu forums.