tuedel@tuedel-o-mat:~$ speaker-test -c6 -Ddmix6 -twav

speaker-test 1.0.14rc2

Playback device is dmix6
Stream parameters are 48000Hz, S16_LE, 6 channels
WAV file(s)
Sample format not available for playback: Invalid argument
Setting of hwparams failed: Invalid argument
tuedel@tuedel-o-mat:~$ speaker-test -c6 -Dplug:dmix6 -twav