What have you tried using to stream Netflix? If you've got an app-enabled television, the Netflix app there might be capable only of stereo.
One person on this thread writes:
Another poster on that thread quotes a Netflix support tech as saying the Netflix plugin for MCE, the Silverlight plugin, and other browser-based streaming is also forced downmixed to stereo. He says:
So,
@moves, since it's probably not a problem of bandwidth, could it be the player that resulted in your negative experience? If not, then avast yeh skallywag.