I have a digital output from my linux box to my amp. I can play dvd in 5.1 surround perfectly and also stereo to amp fine using amarok with alsa and the device "plug:surround51:0". What I would like to do is use the two rear channels when playing my music. I have googled and see you can edit /etc/asound.conf file with the following:

pcm.!default {
type hw
card 0
device 1

pcm.dup {
type route
slave.pcm surround51
slave.channels 6
ttable.0.0 1
ttable.1.1 1
ttable.0.2 1
ttable.1.3 1
ttable.0.4 0.5
ttable.1.4 0.5
ttable.0.5 0.5
ttable.1.5 0.5

pcm.dupl {
type plug
slave.pcm "default"
slave.channels 6
route_policy duplicate

I then change my stereo device in Amarok to read "plug:dup" but nothing. Amarok does not complain and the it appears to play ok, but silence.

I also have run "speaker-test -D dup -c6" it runs without complaint but no sound ! if i run it with -c2 it work fine and I get sound, very strange

Any suggestions of where I am going wrong would be great.