i have the same issue as you but using Creative Super X-fi amp/DAC instead:
If Even hammerhead won't work means the issue is with Poweramp end i guess....
Device model- Razer Phone 2+Creative Super X-fi USB DAC/AMP(Chip: AKM AK4377 )
ROM version- Stock Rom
Why do you think your device supports Hi-Res- https://sg.sxfi.com/products/sxfi-amp