This page does include information not relevant for current OpenWrt releases.
is required (uClibc-0.9.32 in trunk includes this)
libtool2 is required (also available in trunk only, since 2011-01-30)
support or a native soundcard-driver is only needed if the device should play audio locally.
OpenWrt Backfire-10.03.1 doesn't have the necessary uClibc-NPTL/libtool2 stuff. Therefore you can't use pulseaudio with backfire.