I figured it out, after doing stuff as crazy as going to an EMI isolation room (RF/WiFi testing), and it's /facepalm I didn't see the common factor. I run everything balanced. On a whim, I used a 2.5mm to a 3.mm. The hiss dropped very very low - to the point I had to max volume to hear it. Back to balanced, and bam! I can hear it again. To be clear, it's not "hiss" in the purely pedantic definition, but "noise". Slight pop when DSDs start. With Poweramp beta, I got the pop when it was scanning and I kicked off playback. Less prevalent once done scanning - only with DSDs, not with AACs from iTMS. Edit: Do you with the unit hear the slight pop/crackle when music starts? It sounds exactly like my Android phone with UAPP/Poweramp. It's not evident on my Sony Walkman.