I use Ubuntu with an external, USB-connected DAC. For a long time, changing the output volume setting in Sound Preferences had no effect of the sound coming out of the speakers. The sound was either mute, or at a constant volume. I revisited this problem yesterday and discovered a solution: In the Hardware tab of Sound Preferences, I could change between four profiles for my DAC: Off, Analog Mono Output, Analog Stereo Output, and Digital Stereo Duplex. Changing this setting to Digital Stereo Duplex made the volume control work as expected.

That was yesterday. Today, I lost control of the volume again. I revisit the Hardware tab in Sound Preferences, and there is no longer a Digital Stereo Duplex option available.

I performed a system update yesterday, so it's likely that the setting was removed due to an updated package. Any clues as to what package this was, and how I can recover this setting?