April Music Stello U3 play guide - Manual (Page 4)

2) Output Device – WASAPI Installation
Please go to http://www.foobar2000.org, click ‘component’ at the
menu and download ‘WASAPI output support 2.1’
Please save the downloaded file into C: → Program Files → foobar2000
→ components.
Please go to above folder and check if there is ‘foo_out_wasapi.dll’ in it.