@Shanling it seems I'll need some more help. If you recall, a few weeks ago my first M0 player stopped communicating with external DAC's out of nowhere (at one point it just said "Audio Disconnected" while successfully playing, and since then it no longer connects to any DACs). I've been using my second M0 player for the last two weeks and now it won't connect to any DAC either. The events leading up to the issue are different on the second M0 though. What happened this time is that I connected the M0 to my Fiio E17K and, in my mistake, I forgot that the E17 had USB charge set to "ON". When the M0 was connected the E17 attempted to charge from the M0, the M0 battery indicator immediately went red, and then the M0 said "Audio Disconnected". Now the M0 no longer connects to any DAC. Just like my first unit, everything works as expected except the external DAC feature. I've attempted all the normal troubleshooting (factory reset, pin reset, removed card, etc...).
Could you ask the developers again as to if there is any way for this to be a software issue, where the external DAC feature gets stuck? Both of my M0's are past the return period, so I'm realllly hoping that some future firmware change could fix my units.