tuedel@tuedel-o-mat:~$ speaker-test -c2 -Dplug:ch51dup -twav

speaker-test 1.0.14rc2

Playback device is plug:ch51dup
Stream parameters are 48000Hz, S16_LE, 2 channels
WAV file(s)
ALSA lib pcm_direct.c:1632:(snd_pcm_direct_parse_open_conf) Unknown field format
Playback open error: -22,Invalid argument
ALSA lib pcm_direct.c:1632:(snd_pcm_direct_parse_open_conf) Unknown field format
Playback open error: -22,Invalid argument
ALSA lib pcm_direct.c:1632:(snd_pcm_direct_parse_open_conf) Unknown field format
Playback open error: -22,Invalid argument