Já experimentou o módulo snd-dummy?
$ modinfo snd-dummy
filename: /lib/modules/2.6.28-11-generic/kernel/sound/drivers/snd-dummy.ko
license: GPL
description: Dummy soundcard (/dev/null)
author: Jaroslav Kysela <[email protected]>
srcversion: AFF1C8B79BA4E7C29AE9874
depends: snd-pcm,snd
vermagic: 2.6.28-11-generic SMP mod_unload modversions 586
parm: index:Index value for dummy soundcard. (array of int)
parm: id:ID string for dummy soundcard. (array of charp)
parm: enable:Enable this dummy soundcard. (array of bool)
parm: pcm_devs:PCM devices # (0-4) for dummy driver. (array of int)
parm: pcm_substreams:PCM substreams # (1-16) for dummy driver. (array of int)