From Documentation/sound/alsa/OSS-Emulation.txt in linux-2.6.11-rc5: Only necessary step for auto-loading of OSS modules is to define the card alias in /etc/modprobe.conf, such as alias sound-slot-0 snd-emu10k1 As the second card, define sound-slot-1 as well. Note that you can't use the aliased name as the target name (i.e. "alias sound-slot-0 snd-card-0" doesn't work any more like the old modutils). The Gentoo ALSA guide contains references to "alias sound-slot-0 snd-card-0" - they need to be changed to "alias sound-slot-0 snd-via82xx" or ALSA OSS emulation will not work (no /dev/mixer et al).
i've fixed this a while back, just forgot to mark it as such...