edit and add which speaker makes noise when you run this command:
speaker-test -c6 -Dplug:surround51 -t wav -l1
example: Front Left -> Front Right   #means Front Left sound is from Front Right speaker

edit the following lines to show us what your soundcard doing:
example: Front Left -> Front Left

Front Left -> 
Front Right -> 
Rear Left -> 
Rear Right -> 
Center -> 
LFE (subwoofer) -> 

post the above to #alsa or some pastebin site

some ttable info:
speaker 0 - Front Left
speaker 1 - Front Right
speaker 2 - Rear Left
speaker 3 - Rear Right
speaker 4 - Center
speaker 5 - LFE

asoundrc usage: ttable.<channel>.<speaker> <volume>
example for the VIA8237 soundcard:
ttable.0.0 1    # channel 0; speaker 0; volume 100%
ttable.1.1 1    # channel 1; speaker 1; volume 100%
ttable.2.4 1    # channel 2; speaker 4; volume 100%
ttable.3.5 1    # channel 3; speaker 5; volume 100%
ttable.4.2 1    # channel 4; speaker 2; volume 100%
ttable.5.3 1    # channel 5; speaker 3; volume 100%

# copy from here to the end of this file to /home/$USER/.asoundrc
# .asoundrc for new ttable settings created by gnubien 08-11-07
# comments,additions and corrections are always welcome
# test with this command: aplay -Dnewtable some.2-channel.stereo.wav
# test to see if .wav file is 2 channel stereo with this command: file name.of.wav
# if file returns "stereo" then it is a 2 channel stereo file
# run this command: speaker-test -c6 -Dplug:newtable -t wav -l1
# if speaker-test worked then ...
# run this command: speaker-test -c6 -Dplug:surround51 -t wav -l1
# report problems
pcm.card0 {
     type hw
     card 0
          }

pcm.newtable {
    type route
    slave.pcm surround51
    slave.channels 6 
    #new ttable settings
    ttable.0.0 1    # channel 0; speaker 0; volume 100%                                                       
    ttable.1.1 1    # channel 1; speaker 1; volume 100%                                                       
    ttable.2.2 1    # channel 2; speaker 2; volume 100%                                                       
    ttable.3.3 1    # channel 3; speaker 3; volume 100%                                                       
    ttable.4.4 1    # channel 4; speaker 4; volume 100%                                                       
    ttable.5.5 1    # channel 5; speaker 5; volume 100%
             }
ctl.card0 {
    type hw
    card 0
          }