It is often an HDMI issue. When your source talks to your TV, the TV reports to the source it is only a stereo device. Therefore the source only sends a stereo signal to the TV and that is what gets passed to the optical from the TV. This is very common and not a specific LG issue, it happens with most brands as it is setup that way because of how HDMI does its handshaking. The way around this is to run an optical or digital coax directly from your sources to the sound bar. I don't know how many inputs your LG sound bar has. Then your sound bar will get the full 5.1 signal if your source is configured correctly. This where a good universal remote comes in as you will have to do switching at the TV and sound bar.
Bass management to the subwoofer should be handled by the sound bar for 2.0 signals. It is uncommon for signals to be sent in anything other than 5.1 or 2.0 formats.