If you're ever desperate, you can always just stick your regular headset plug into one of the double sockets half-way (until the first click) and still get audio on both speakers.

Most movies/tv shows are mixed with dialogue on the center channel (or mono), so you'll be all set. I don't ever listen to the music channels on AVOD, so I'm not sure if you only get the left/right side. YMMV.

...or you could just ask for an adaptor