Since I had the same problem (No Sound in Intro Scenes and Cutscenes, but In-Game Sound worked) and none of the suggested Solutions helped me, here is what fixed the Problem for me:
After discovering that with Headphones the Problem did not exist I remembered reading something about different channels in Audio and that i.e. the Sound for Cutscenes goes to a Channel that has no Output in the speakers I tried changing the Audio Mode of my speakers (TV speakers in my case) in Windows.
In my case I had to change them from Stereo to Windows Sonic for Headphones.
For those who don't know how to change the mode. Right-Click on the Speaker symbol in the Task-Bar when at the desktop. Then go to something like Speaker-Setup (my Windows is in German so I dont know the english term, its the Option in the middle). It should already show you in the title something like "Stereo" or "7.1" whatever your setting were. Then just change the setting to whatever else is available and see if it works.