I am using OnePlus 6 with Android Pie and Poweramp@v3-build-803-play. I have been facing issues with the audio output on this specific android version. Note that these issues are not specific to the latest version of Poweramp and have been there for all the beta and RC ones which came before it(maybe the last 5).
Hi-Res Output which used to work fine on android 8.1 stopped working after the OS update. If I have Hi-Res Output enabled, there is no audio output in my wired earphones. If I disable 'Direct Volume Control', I get audio output but I am not sure how this affects audio quality so I am not using it.
With OpenSL ES Output, there is a peculiar noise, a continuous ticker, which is only audible during relatively quiet parts of any song, similar to signal interference. And I have a work around which I have to do every time I (re)connect my earphones. I have to open the audio output settings under 'Settings > Audio > Output > OpenSL ES Output> Wired Headset/AUX settings' and then toggle 'No DVC' twice so in the final state is DVC still enabled.
Update: Issue is still present with v3-build-805-play