https://bugs.winehq.org/show_bug.cgi?id=43173
--- Comment #10 from Ethan Lee flibitijibibo@gmail.com --- Ah, now THAT log is interesting. Particularly the part where it only calls GetDeviceDetails twice, and then never creates a source! This means that it makes a context (which is the SDL device you're seeing), but then does nothing with it, which is why you're hearing silence. In fact, it seems to do a whole bunch of work with DirectSound instead. This may explain why setting the OS to WinXP fixes the issue for others. I would try that next and see if setting XP makes it ignore XAudio2 altogether.
Even more interesting is that the bug may be with the games themselves; googling "Far Cry 4 XAudio2" brings up some results regarding specific driver configurations that cause the game to be silent even on Windows. I've not seen this before when looking up XAudio2 behavior/usage for other games, so we're mostly likely looking at an engine bug. I'll have to see if I can figure out a device configuration that the Ubi sound engine likes...