Thanks! Unfortunately I have returned the DX120 to Zeppelin, so I don't have it with me now. For the demo unit that I reviewed, it seems there wasn't any plastic protector over the back side, but I will double check when I go to Zeppelin. Maybe it was early batch unit for demo? I'm not so sure about that. I measured the frequency response and digital filters in both firmware version V2.1.20 (22 September 2018) and V2.2.42 (28 October 2018), and all same result. Yea I'm curious what Paul will comment about the digital filters in USB DAC mode. In DAP mode they are working fine.