Peviously, when adding a missing tool, I had gone into Tools->Choose Toolbox Items, then selected a missing component.
In your Demo project, for example, you can see your NAudio tools (widgets/components) available within the .NET Framework Components tab within the Choose Toolbox Items popup form.
I do not have those NAudio tools available to add from within my new Project's Choose Toolbox Items->.NET Framework Components list. Perhaps I am not properly including the NAudio namespace or Assembly or something.