[PROBLEM] Problem with an SMSL M300SE DAC

[TheOldPresbyope]

Such a quick response, I'm happy. 

@ Nutuil :The alsamixer shows x- default / x0- HDMI / Headphones (screenshot). Does that mean default is my DAC?

@ Tom Curtis & TheOldPresbyope: Yes, currently the HDMI port is selected. But I only have HDMI and headphone jack to choose from. 

This all looks to me like the device is not recognised as an audio device. Is that correct?

Sadly, I think you are correct.

Your DAC (even if identified as the serial converter) should show up in both places if Linux can figure out it's a USB audio device.

And no, the default isn't your DAC. If you select it, you'll probably find the default is the HDMI port. That's true in my case, even with my Khadas USB Tone1 board selected as the moOde output device.

Regards,
Kent