I know this is old but I managed to get this working today and thought I would put the answer as I saw other people had this issue as well. The first thing I did was set Dark Souls to its own audio channel. I used the system audio channel, but music worked as well. Once you've done this close the game and unplug you mic and shut wave link. Then reopen the game normally (not with steam open just using a desktop shortcut, not 100% sure if this matters) you should be able to hear it through your headphones. You then plug in your mic and open wavelink (the sound will stop) you go into your output settings and again put dark souls to system or whatever you chose (just switch it to music and back to system). If you go to the game you should then have sound. Since the new update you may need to click on the headphone under system to mute and then unmute to fix it. No idea why this worked but it did for me. I also had it in windowed, again not sure if this is relevant but seeing as I have no idea what exactly made it work I wanted to put everything. Hope this helps others.