Because of the sound alias in /etc/conf.modules it is impossible to give options to the sound.o module (like dmabuf=1). The initscripts startup sound by looking for this alias (thus changing alias means changing rc.sysinit)
Adding the following to /etc/conf.modules: pre-install sound insmod sound dmabuf=1 should do the trick.
Bill, if this bug is a no-op, close it.
sndconfig-0.31-3 will add this line to /etc/conf.modules appropriately.