4.How can I use USB DAC function?
A: First switch the USB mode to USB DAC (tap the 'Storage' icon in the pull-down shortcuts menu to switch or enter Settings -> Audio -> USB mode to select). After that, connect the M11 to the computer via USB and use it as USB DAC. ( Before using on Windows computers, you'll also need to install the DAC driver, which can be downloaded at click here; for Mac computers, there's no driver required).
Here is the video instruction(take M15 as a example):