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%