Since the P180B case says it uses AC 97, shouldn't I use AC 97 in the BIOS? In any event, I had tried HD Audio in the BIOS, as that was the default setting. That didn't work.
There's a cable from the case front panel with the "standard" 10-pin Intel connector, which I have plugged into the Audio pins on the motherboard.
I'm thinking of just getting an external switch. That may actually be more convenient anyway.