http://www.mudcat.org/threads.cfm?mixbs=yes is supposed to do it if one is not logged in (from FAQ)...

BS-viewing options if logged in (click MEMBERSHIP up in the topmost page banner):

BS filter Yes No If "Yes," filters threads designated "BS / non-music" out of Threads listing

Mix Music & Non-music Yes No If "Yes," mixes music and non-music threads in the Threads listing

~S~