hi,
even onboard sound cards supports 4.1 & 5.1 channel audio. mine is intel 865 MB. it has an option called "Multi-Channel sound Manager". using this you can get 4.1 & 5.1 channel audio. this is possible as the software converts the mic & line-in jacks etc into speaker out jack.
i think even 845MB has this option. see in your MB cd.
thank you.