@cha0z_ On my (same-soc) S9+ it works OK for Pie update and I guess generally ROM/firmware/audio subsystem is the same, so it must be something with your settings. You haven't specified what output you use, though (BT or wired or else), and these are completely different outputs with completely different tweaks and issues (the wired output is own Samsung implementation which differs from any other OEM/stock Android, the bluetooth part is Google based with tweaks by Samsung).
Requests for Hi-Res Support (please state which build of Poweramp you are using)
in Poweramp Feature Requests
Posted
I use Bluetooth and mine says 16 bit still, what Bluetooth settings do you use max , in developer options perhaps??