The newest updates to Windows 10 contain privacy and security settings for the usage of your machine's microphone. These settings will block SS's access to your microphone when trying to record system audio. Here is what you need to do to solve this issue.
Go to Windows 10 Settings > Privacy > Microphone then toggle "On" "Allow apps to access microphone" and scroll down page and toggle "On" "Allow desktop apps to access microphone" then open Song Surgeon > Record > Recording Devices. In the "sound" window look for ( depending on what you want to use ) "Stereo Mixer" or "Microphone". If you don't see Stereo Mixer or Microphone, right click in sound window and select "Show disabled devices" and "Show disconnected devices" now right click on "Stereo Mixer" or "Microphone" and click "Enable".