I have the same issue, I'm using Power Amp build 703 with "Samsung Level U Pro ANC" on my Galaxy S7 (SM-G930FD). The issue with "stuttering" sound persists on any Audio Output (Hi-Res, OpenSl Es) and with any buffer size, I've tried the maximum. I've also tried various sample rate on Hi-Res. Would you please assist with this? Probably it is needed to increase Poweramp process priority or something else, but I haven't root on my device.
P.S. I am on the latest released Android 6.0.1. SD card is absent, all music are in phone memory