grants ~ # speaker-test -twaw -D ch40dup -c4

speaker-test 1.0.14

Playback device is ch40dup
Stream parameters are 48000Hz, S16_LE, 4 channels
WAV file(s)
Broken configuration for playback: no configurations available: Invalid argument
Setting of hwparams failed: Invalid argument

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grants ~ # speaker-test -twaw -Ddefault -c2

speaker-test 1.0.14

Playback device is default
Stream parameters are 48000Hz, S16_LE, 2 channels
WAV file(s)
ALSA lib pcm_params.c:2152:(snd_pcm_hw_refine_slave) Slave PCM not usable
Broken configuration for playback: no configurations available: Invalid argument
Setting of hwparams failed: Invalid argument