My Mac audio goes out via USB to my Massdrop SDAC-B which goes into my THX789 amp for my headphones. But this issue is more recent. I've has this setup for about a month now.Usually I see this message when I'm having some kind of audio problem (usually over HDMI from an RX 480.) You could try a different audio device (e.g., your Mac's onboard audio or a USB sound card) or try plugging headphones into your headphone jack.
Are you trying to play sound through anything other than your Mac's built in speakers?
Its entirely possible that one of your audio devices decided to start glitching out after you set it up. Or it could be a bad cable, or not even audio related at all. That's why you need to start eliminating the possibilities, one by one.I've has this setup for about a month now.