iphone remote app volume control issues

I was PSYCHED when my Apple tv 4th gen allowed me to control the volume via the iphone remote! FREEDOMMMMMMMM!!!!! (from remote controls). I HATE remote controls!
BUT, volume control [on the iphone app] only works when I pair the ATV4 via bluetooth to my soundbar. That's a problem for me because no matter how much I struggle with the tv and the soundbar which both have sync settings, I can't get the volume to match up and I feel like I'm watching old badly dubbed kung fu movies (and the kung fu movies all match up perfectly, RUINING the effect btw).
So I plugged my tv into the soundbar with an optical cable (it doesn't have hdmi) and the sync issue is gone, it matches up perfectly! (but not the kung fu movies, which means it's working). BUT, like some sort of dark magic, the volume buttons on the side of my iphone stop controlling the volume I hear from the movie. Don't get me wrong, there's still volume, I just can't turn it further up or down at all from the iphone app. So, during quiet parts of the movie where the hero is contemplating whether his path of vengeance is righteous, or, when there's a part that's too loud, like his enemies screaming in pain, I have to find and reach for some other remote than my iphone!

It's supppper frustrating! Please give advice. What's the best way to regain control of my ability to change the volume from my iphone app, while not having to deal with audio sync issues?


TLDR/Visual learners:

[SOUNDBAR]<---bluetooth---[APPLE TV]---hdmi-->[TV] = Volume buttons on iphone remote app work

[APPLE TV]---hdmi-->[TV]---optical--->[SOUNDBAR] = Volume buttons on iphone remote app DON'T work.