You may find that you prefer using the soundbar for regular TV too, not just for movies. It should certainly provide a better audio experience than the TV speakers. To do it that way, just connect the sat box via HDMI directly to the soundbar, then run another HDMI from soundbar's ARC port to the TV's ARC port. Look in your owner's manuals to see what settings are needed to enable HDMI-CTL (CEC).
If you really don't want to use the bar for normal TV, then I'd suggest you connect the sat box directly to the TV. The rest of this suggestion is guess-work on my part since I don't have an LG. Connect bar and TV via the ARC ports (as above). If you don't turn the bar on, the LG should use its own speakers. When the bar is turned on, the LG should mute and send audio to external. That may or may not work between the two different brands. If it doesn't, you could run an optical cable from TV to soundbar, but you might have to change the LG's audio settings whenever you want audio going out to the bar. You'll just have to try your options and see what works.
If it was me, I'd just connect sat box to bar and always use the bar.
Thanks very much for the help. Will my sound suffer due to hooking up each unit to the TV rather than running them through the sound bar?
Also, I've got an optical cable ran behind the drywall. I was going to use that from the TV to the sound bar. But you suggested I used HDMI cable. Will that make a difference, or is my optical cable ok?