SoundTap isn't recognized as an output device, SoundTap is an installed program that will capture the audio being played on your computer and save it to where you set it by going to SoundTap > Preferences > Recordings Folder.
To use SoundTap, play some audio on your PC, then click the "Start Recording" button, when finished click the button again, this time "Stop Recording". to Check the recording go to "Find & Play" or go directly to the location you set up as "Recordings Folder".