I think there were only a limited selection of 2011 models that had the presence sensor, with a strange distribution. It was available on some lower-end models, and the very highest LX range, but not most of the mid-range sets if I recall correctly.
All of Sony's models offer a "Picture Off" power saving mode, but it's several layers deep in the menus (Menu > Settings > System Settings > Eco > Power Saving > Picture Off) so it may as well not be there.
They also have an "idle standby" option that can be set to turn off the TV after 1, 2, or 4 hours of inactivity. A message pops up on-screen for a couple of minutes and if you don't press any buttons on the remote, the set will switch off. Unlike the old sleep timers where you had to keep pressing a button to set a countdown timer, this is always on once set.
If all you are wanting is audio, you should be able to set up any TV to have a picture that is very dim (having a picture that is very dim, but still looks good is a different thing) and depending on what it is you're trying to watch, you could probably just hook up a set of speakers or headphones directly to a set-top box or other device's audio output and bypass the TV altogether.