Who knows? You see the results above. There's a lot spurs that aren't harmonics of 10kHz on the E50. The Modi+ and Zen V2 (that uses an ancient chip) are far cleaner and what I would expect. And they don't even have the benefit of the 128db SINAD OPA1612. As you said, the onboard chip filters are fine. Also, I just cannot see ESS engineers (who design the onboard chip filters) to bork things this badly. I would be curious how an E50 without the ultrasonic crap would sound. It could be pretty good.