I would love to know if you manage to do it, I havn't started my carpc yet, I am still looking for the right soundcard to do the job (and for the monitor, and for the 80g drive for the laptop...).
I assume that other than having jack + LADSPA you need a soundcard supporting this 4.1 output. Do you have one?
All I want is Left-right-front-rear balance + SW level and maybe SW cross control. just the same way I control it now on my pioneer HU...
Thanks and good luck.