I know well how Rocksmith 2014 is not friendly with audio interfaces. If you can unplug that interface/mixer, I would try that first. If you can't, I would recommend trying this: right clicking the volume thing on the task bar and going to "Sounds" and not "Open Sound settings". Then click on Headphones/Speakers, how ever it comes up, and then clicking the "Set Default" button. If that doesn't work, go to every device besides your headphones in "Sounds" and open up the properties menu and at the bottom of that menu, toggle "Use this device" to "Don't use this device". I find it hard to imagine windows will switch to those devices if they are disabled, but ya never know.