I have a Direct Stream DAC connected to a Mac Mini running JRiver MC24. Connection is via USB. Periodically (maybe 3 times) in the past I am confronted with a situation that I never seem to have a clear resolution to. The problem is that there is no sound from the DSD to the preamp. The DSD shows the proper file resolution for the song I am playing, but there’s no output. The optical input from a TV is OK. I usually start trouble shooting by checking in MC24 that the PS Audio DSD is selected as the audio device. Then I proceed to the Mac Audio MIDI Setup & check that the DSD is recognized as the output device. (not sure if this is relevant???) Then I look to see if anything obvious has changed in MC24 Audio Device settings. Not sure what I’m looking for, but I keep hoping something will be obvious.
As mentioned, this has happened before after a power outage & I usually just reestablish the relationship between the DSD & Mac. I never get a memorable ah-ha that was it because I try several things before restarting MC24 & Mac. Any sort of list of checks would help me immensely. I promise to write it down this time. 
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Edit: Solved! Under Audio MIDI Setup > Master Stream, Master, the Mute was checked!
I did not do this. Could it have been the result of a Mac OS update. Can’t remember if I have listened since the update??? Does not the optical input follow the same path? It was fine???
Please feel free to comment on this, as I don’t really understand what happened???
Thanks,
Kev