Sony KP-57WV600 Operating Instructions Manual page 42

Usi.ng the TV's
Audio Menu, set the Speaker option to Off. Then set
the Audio OUT option to Fixccl or Variable, depending on how you want
to coni.roi the volume. For details, see "Using the Audio Menu"
on page 74.
'rum on the audio
receiver, and then set the receiver's line input
to the jack into which you connected the TV.