Wait what, I had some success yesterday evening with this, now the volume in the top speaker changes significant more but I didn't push the build yet XD
@NeoArian did you find a general solution for that? So far I looked at the mixer_paths config files (found no issue there) and started to look at the msm8974 kernel audio driver. Now I wanted to dig into that a bit deeper but then saw your post here. I can also do some A/B tests today if you like.