https://bugs.winehq.org/show_bug.cgi?id=37957
--- Comment #5 from hellas@burntcomma.com --- Thanks Sebastian.
Comment #0 - your best bet is to use Pulseaudio, with the winepulse patches in wine-staging. You can then use pavucontrol to force your card into stereo mode. Failing that, I think what you want is to pass a stereo-only model to snd-hda-intel (if that's what you're using), something like 3stack or similar. I think you also have to make sure that you specify the output device in winecfg, as IIRC "(default)" always has six channels.