Thanks Blaise,

Seems that sound_play will only pick up my Festival default voice if it
is set to don_diphone in the file /usr/share/festival/voices.scm.  If I
set it to any other voice, I get the odd demon voice from sound_play
(thought it works for Festival).  But at least I can get the don_diphone
voice to work.  I'll look more into the Festival command line options
before adding a note to the ticket you pointed to.

--patrick