Hello. It's like threads gravedigging, but just a week ago I finally brought my pro1 to life by replacing a broken display with Ulephone U one bought on ali (and it didn't require any "firmware update for the touch function to work correctly").
But the point is that just a few moments ago I think I managed to solve problems with too loud handset sound volume and distortion. I replaced "/system/vendor/etc/mixer_paths_tavil.xml" with a file from latest Google Pixel 2 LineageOS (it shares the same MSM8998 CPU). I didn't have much time to test it thoroughly, but sound seems to be much better.