I have been using Poweramp as my only mean of listening to music for almost 5 years now!
That being said, after the Poweramp v3 704, and when playing music through the Hi-Res Output (Experimental) option (at 192K), there is a massive and nasty distortion in the sound, especially while using the pre-amp. It exists even after disabling the pre-amp, and it's annoying. Note, that this distortion does NOT exist on any v3 version from 704 and lower. I can pump up the pre-amp to maximum, with 0 noticeable distortion.
I use the Hi-Res Output since have a relatively high-quality DAC, the Topping NX4 DSD (Not the NX4 variant that doesn't have DSD). The distortion exists whether or not I use the DAC or connect the headset directly to the phone. I even tried other pairs of headsets, but the problem still persists. Clearly, it's a problem from the software side. I have been waiting for a fix for God knows how long. And I didn't want to upgrade my phone to Android Oreo (currently on Android 7.1.1), so that I can continue to use the Poweramp v3 704 version, as it works best, in terms of sound quality.
Here are a few extra details:
My phone model: Samsung Note 8 Duos (international, SM-N950F)
Android: Android 7.1.1
Hope to see a fix in the coming versions rather soon!
Best wishes, and keep up the great work