Sound output problems with OS Monterey to external DAC

I'm experiencing a strange problem since updating my iMac (Retina 5K, 27-inch, Late 2015) to OS Monterey. I had been streaming music to a stereo system from my Mac through USB connected to a Benchmark DAC3 B using Qobuz, Tidal, and Apple Music. The computer is hard-connected to a FiOs router through an ethernet cable (not wifi or bluetooth) and everything had been working great prior to the move to Monterey, but now none of the apps will send sound to the DAC. The connection is still there, since the DAC will show changes in bit rate settings coming from the source, but no sound. If I connect the USB cable from the DAC to my MacBook running Sierra, it works fine, so it's not a problem with the DAC or the stereo components. If I switch to a different USB sound output that connects to external computer speakers, all of the apps work fine, so the problem seems to be limited to the Benchmark DAC.

I've tried resetting the connections and settings, restarting all of the components, restarting my Mac in safe mode, but nothing has worked. I contacted Benchmark and they are unaware of any issue, and since there is no installed driver to use the DAC with a Mac, there is no new Monterey driver or anything to reinstall.

Any thoughts, or has anyone experienced any similar problems? This seems to be very specific to the Benchmark DAC, but it certainly seems to be caused by something in the new OS, so I'm kinda stuck.

Thanks in advance for any advice.

Best,

Jay