This is strange because Visual Studio 2013 does not allow me to manage .dsoprojx projects. I'm able to do it with Visual Studio 2008. I have DeepSea Obfuscator 4.20.65. Are you sure?
It seems the software isn't compatible with the Visual Studio 2013 version. According to the features page, you can install it only on the following Visual Studio versions: Visual Studio 2005, 2008, 2010, and 2012. You can check that on the Feature page offered by the developer.