user@deimos:~$ cat .asoundrc 
# 6 channel dmix:
pcm.dmix6 {
     type dmix
        ipc_key 1024
        ipc_key_add_uid false
        ipc_perm 0660
        slave {
                pcm "hw:0"
                rate 48000
                channels 6
                period_time 0
                period_size 1024
                buffer_time 0
                buffer_size 5120
        }
     }

user@deimos:~$ speaker-test -c6 -Dplug:surround51 -t wav

speaker-test 1.0.11

Playback device is plug:surround51
Stream parameters are 48000Hz, S16_LE, 6 channels
WAV file(s)
Rate set to 48000Hz (requested 48000Hz)
Buffer size range from 3 to 5461
Period size range from 3 to 5461
Using max buffer size 5461
Periods = 4
was set period_size = 5461
was set buffer_size = 5461
buffer to small, could not use
Unable to determine current swparams for playback: Input/output error
Setting of swparams failed: Input/output error