Gnus uses rule variables to decide how to view a file. All these variables are of the form
(list '(regexp1 command2)
'(regexp2 command2)
...)
gnus-uu-user-view-rulessox to convert an .au sound file, you could say something
like:
(setq gnus-uu-user-view-rules
(list '("\\\\.au$" "sox %s -t .aiff > /dev/audio")))
gnus-uu-user-view-rules-endgnus-uu-user-archive-rules