not 100% sure what you meant.
MB already supports multiple artists and in the track browser the artist is split eg. a track assigned to 3 artists will show the 3 artists separately in the Artist panel and each artist will show the track if clicked
How is that done? Is an APEv2 comment with "ARTIST_2" "ARTIST_3" etc ID inserted? Or there's logic to separate artists in the same comment where commas exist? What infogulch wants, if I understand, is to create a library filter to only display files that have multiple artists in their tags.
By the way, infogultch, how are the multiple artists tagged? Are they lumped together in the artist tag (e.g. "Wagner, Liszt, Metallica") or using different artist tags?