I am having the exact same problem as you with the ALC889 chip on two different Gigabyte boards. But unfortunately, installing the old 2.36 driver version, which I found online doesn't solve the issue for me.
I was wondering if you could elaborate a little if there was anything else you might have done, and also, what exactly you mean by "works fine". Do you actually get the "Dolby Digital Live 5.1" output option in the Realtek HD Audio Manager?
Thanks for your help.