Volume control moves to what the optical sent the audio to. Very few LG remotes control everything. There are better remotes like the Logitech Harmony that consolidate remotes.

This is where it's time to try the usual setup of all HDMI sources to the receiver for audio work and then the last HDMI link from the receiver output to the HDTV's ARC and CeC port. Sometimes CeC (see google) works and pulls it all together.