My CCK worked flawlessly with my dac and having a great time with apple lossless. Their audio quality keeps improving over time and have seen the same on many albums i have bookmarked.I faced the similar problem. And found out the issue is with the usb cable when I connected using a audio usb cable. Initially I used a printer cable and it didn’t work when I used it to connect my PC as well. Do check your cable is working when you connect something like a PC or laptop to your amp.