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

speaker-test 1.0.14rc2

Playback device is duplicate
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
tuedel@tuedel-o-mat:~$ speaker-test -c6 -Dplug:dmix -twav

speaker-test 1.0.14rc2

Playback device is plug:dmix
Stream parameters are 48000Hz, S16_LE, 6 channels
WAV file(s)
Rate set to 48000Hz (requested 48000Hz)
Buffer size range from 2048 to 6144
Period size range from 1024 to 1024
Using max buffer size 6144
Periods = 4
was set period_size = 1024
was set buffer_size = 6144
 0 - Front Left
 4 - Center
 1 - Front Right
 3 - Rear Right
 2 - Rear Left
 5 - LFE
Time per period = 8.508141