what distro are you running?
in gentoo, you can put it in /etc/modules.autoload/kernel.<version> This file is just a list, and you can put it in there.
alternatively, you should be able to stick it in the local.start file . This is a file which gets run when the system boots. Should be in /etc/conf.d/local.start (AFAIK). This is a handy file for putting things you want done at startup, like mounting crypt drives.
I'm using Ubuntu. I didn't think it was relevant, otherwise I would have posted it in that forum.
I don't have the file that you describe, but I do however have a /etc/modprobe.d directory with lots of files in it. One of them is named alsa-base, could this be the one? And, if so, should I just add modprobe i810_audio to the end of that file?