Multistar has had an update to version 4.1.02. That should fix your problem.Wow, this worked, thanks. Still, something is different because I remember using headphones used to work on a phone. So now just my first and main reason remains. Maybe you can solve that, too?
I've read all the commnents but I want to be sure I'm understanding it right. You flashed the Korean user T870 on your US version? If so would that mean I can install in on my T-Mobile version of SM-T978U. It wouldn't have the carrier bloat and disabled features like calls and texts on other devices missing from settings?Flashed the Korean T870 version, Used HOME_CSC option to retain my data.
Worked like a charm.