well, I had a look at everything, applied the changes...
I kept using
@shadowstep magisk file rather than using my Magisk template...
I doubt the volume made any difference since the controller was incorrect

, not defined at the top... thus default RX0 value takes 84...
RX* MIX DIGITAL VOLUME mostly for headphones where * is 1 and 2 which are left and right channels... 0 will be ignored...
but I may be wrong because I don't have the original mixer

...
Anyway, now it is set to 96, you should notice the difference...
I added Tags keyword "ear" if anyone wants to navigate through the mixer and experiment...
Channels were set to Two, enabled other controllers...
I hope this fixes everything...
Remember everyone 
If the problem still exists...
Answer the following questions:
1. Do you have a custom kernel...?
2. Do you have another sound MOD installed...?
if the answer is yes, temporarily go back to stock kernel and as for the MODs, do disable other sound MODs...
If both are no, please do a logcat as short as possible with the following :
Play some music, 3 seconds stop it, 2 seconds play, 2 seconds stop... Let someone call you... Answer it, keep the call open for 5 seconds... End the call... Wait for 3 seconds... Stop logging... Attach the logcat in a post with a mention or send it to me here or facebook... I'll have a look, find the problem and solve it hopefully... ?
No worries everyone ...
PS: before logcat that is if it is required, place everything on the home screen, navigating and swiping adds more lines in the log, such a hustle for me ...
I need as short as possible so I wouldn't get lost... ?