1. From Colorfly's C10 web page,
'USB - DAC drive, techenique team is improving, please be patient.'
Link below:-
http://www.colorfly.net/downloadc10.html
I will suggest you not to have any high hope of waiting for Colorfly to ever come up with a solution on USB DAC function for C10.
2. UI and features wise, unfortunately, C10 is rather 'primitive'.
But as for shuffle, I thought C10 handles shuffle the standard way like how most DAPs would do it.
Example, you have many sub folders (Dire Straits-Money For Nothing, Adele-25, Ed Sheeran-Divide, etc, etc) under a main Rock Folder.
If you select the final folder Adele-25, C10 will only shuffle songs within the Adele-25 folder.
I thought this is correct.
Or am I wrong?