I installed the latest drivers on the Realtek site, and since then, only the rear speakers have worked. I've fiddled around with the settings to no avail.
Nevermind, I got it working. I had the jacks custom-configured and the new installation didn't keep the old jacks config. Also, turns out that the new software doesn't like the matrix button on my centre speaker; if that button is pushed in, the centre speaker and subwoofer don't work at all.