Try this:
Edit dialog with Multiples selected, search mode as Word not String, on the Match row select only Artist & Genre buttons, I don’t know why but just selecting Artist only finds a few
On the Yes/No fields select Just Karaoke. If you also have Audio, Video & Kvideo you want to include Try them separate after wards I only tried this with Karaoke types.
Now in the search field enter * & * make sure to enter a space between characters and press search.
Now I don’t know if it finds all but my test produced a lot of results.
I attach a screen shot showing my settings to make it clearer.
One note though, not all songs with & in the artist field are true duets having the start of the track showing different colors for each singer.