While I know a fair bit about general use of Poweramp, I've never delved into the black arts of the API and sending Custom Intents. I've just upgraded my Samsung Note phone from KitKat to Marshmallow and so much is no longer the way I want it, or is just plain broken, including using my three-button headset +/- controls for track and album access while the phone is in my pocket.
I've found an Xposed Module (PBMC Key Chains) that with a bit of tweaking gets me 90% of the way there, and I can issue single-click MEDIA_NEXT and MEDIA_PREVIOUS key scancodes, plus use long-press for MEDIA_REWIND and MEDIA_FAST_FORWARD, which only fire while the screen is off. However there does not seem to be a key scancode that causes Poweramp to execute a Next List or Previous List action (for switching albums, folders, etc).
What I can do is issue a "Custom Intent URI" though, which means I need to work out how to format such a command (the editor for such commands is a plain text box). I believe I need to create something along the following lines:
Extra: cmd:6 ('6' for next item in category, '7' for previous item in category)
Does that seem correct and complete, or have I misunderstood the docs? It doesn't seem to work when I enter that into the Custom Intent URI box anyway.