http://bugs.winehq.org/show_bug.cgi?id=12182
--- Comment #39 from Ákos Maróy akos@maroy.hu 2012-11-19 02:55:09 CST --- you guys are, well, quite arrogant.
anyway, for some reason the sound works now. how I got it to work is that I used a 32-bit manually compiled version of wine to install XCOM & related dependencies using winetricks, including xact. (version wine-1.5.13-402-gcd9451c to be precise). interestingly, this wine wouldn't run XCOM itself, but the 64 bit wine that comes with ubuntu 12.10 (wine-1.5.16) runs it with sound afterwards.
I'm not sure how the above wizardry made it work though.