Find correct CMUS alsa device configuration for volume control

I have a raspberry pi with an IQAudio DAC+ hat installed, running the Volumio linux distribution. The card works well. I've set the dsp.alsa.device setting to device:1 and this outputs the audio correctly over the DAC hat. But the CMUS volume control doesn't work. I think I have to set mixer.alsa.channel and mixer.alsa.device in CMUS. Right now, they are set to mixer.alsa.channel PCM mixer.alsa.device default What device name and channel name do I use? I've tried these combinations: mixer.alsa.channel PCM mixer.alsa.device default:1 mixer.alsa.channel Digital mixer.alsa.device default:1 mixer.alsa.channel PCM mixer.alsa.device IQAudioIODac mixer.alsa.channel Digital mixer.alsa.device IQAudioIODac mixer.alsa.channel PCM mixer.alsa.device default:CARD=IQaudIODAC mixer.alsa.channel Digital mixer.alsa.device default:CARD=IQaudIODAC But CMUS always gives the error message Error: can't change volume: mixer is not open. Should I use a different CMUS setting? Here's my output from aplay -l: card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA] Subdevices: 6/7 Subdevice #0: subdevice #0 Subdevice #1: subdevice #1 Subdevice #2: subdevice #2 Subdevice #3: subdevice #3 Subdevice #4: subdevice #4 Subdevice #5: subdevice #5 Subdevice #6: subdevice #6 card 0: ALSA [bcm2835 ALSA], device 1: bcm2835 ALSA [bcm2835 IEC958/HDMI] Subdevices: 1/1 Subdevice #0: subdevice #0 card 1: IQaudIODAC [IQaudIODAC], device 0: IQaudIO DAC HiFi pcm512x-hifi-0 [] Subdevices: 1/1 Subdevice #0: subdevice #0 And here's my output from aplay -L: hw:CARD=ALSA,DEV=0 bcm2835 ALSA, bcm2835 ALSA Direct hardware device without any conversions hw:CARD=ALSA,DEV=1 bcm2835 ALSA, bcm2835 IEC958/HDMI Direct hardware device without any conversions plughw:CARD=ALSA,DEV=0 bcm2835 ALSA, bcm2835 ALSA Hardware device with all software conversions plughw:CARD=ALSA,DEV=1 bcm2835 ALSA, bcm2835 IEC958/HDMI Hardware device with all software conversions default:CARD=IQaudIODAC IQaudIODAC, Default Audio Device sysdefault:CARD=IQaudIODAC IQaudIODAC, Default Audio Device dmix:CARD=IQaudIODAC,DEV=0 IQaudIODAC, Direct sample mixing device dsnoop:CARD=IQaudIODAC,DEV=0 IQaudIODAC, Direct sample snooping device hw:CARD=IQaudIODAC,DEV=0 IQaudIODAC, Direct hardware device without any conversions plughw:CARD=IQaudIODAC,DEV=0 IQaudIODAC, Hardware device with all software conversions