You mention that you manually installed the driver, please can you confirm that you are using Mix Control 1.9b10 with the 3.2.1 driver?
Or Mix Control 1.9b4 with the 3.2.1 driver?
It's unusual that you're having playback issue, we haven't seen any such playback issues that directly relate to the Windows 10 element of the setup.
Do you have the same issue across all the USB ports?
Let me know how you get on.
Simon // Focusrite Technical Support
[ Post last edited on 07/31/2015 at 02:19:55 ]