When I upgraded to Mavericks I noticed that I was no longer hearing audio when playing video files (i.e. .wmv, .mp4, .mov, .mkv, etc.), but this was only happening while using my Razer Kraken 7.1. I also discovered that the headset was receiving audio just fine from streamed videos via the browser (i.e. Netflix, YouTube, and Simple.TV). This led me to believe the problem was with my video player, but after testing it with a few others (i.e. MplayerX, VLC, and Movist), I was getting the same result. I then decided to uninstall Synapse... Once uninstalled and restarted, the issue was resolved. I contacted Razer support and this is what they sent me. I had since did a clean install, but followed the directions as they applied to me. This did not resolve my issue. Installing Synapse basically re-creates the issue. While searching Google, I have found other users reporting similar symptoms, but the culprits were other sound software (i.e. Boom and SoundFlower), but I don't use either. I have since replied back to Razer Support, but I am not holding my breadth. Something leads me to believe there is some sort of bug or compatibility issue with Mavericks and Synapse (and possibly other similar sound software). Figure I would post here and see if anyone had a take on this situation.