Well, ALSA (www.alsa-project.org
) seems to be the way to go if you can get it installed and want the most up-to-date drivers. But that's what I'm using and still only get 2-channels with an AD1980. I've tried the other jack sockets also. There is quite a bit of info about status of individual chips on that site.
A lot of onboard chips just use the intel8x0 driver, which I think only uses older, backward-compatible features of these chips. Maybe the driver writers figure the audience is not big enough for the effort needed to write new drivers for every chip, or maybe the manufacturers are not releasing enough details to make it possible.
But SB Live and various successors have a big following, so I think their drivers have more features in this area.