Ah yes, the MB4 Midi Bass....talk about unicorn! I have one too, a 4string...a glorious instrument, but wish mine were a 5er.
Has anyone been able to use one in poly mode? I'm using mine with a Yamaha Motif sound generator (the rackmount brain model of the keyboard), and in poly mode it splits the instrument to two different sounds; like strings and drums. Not what I want, when I'm trying to get chorded strings or piano etc.
I can accomplish the chorded intervals externally via pedals, but I'm trying to do this with just midibass and sound module.
Finding info on these rare beasts have just been deadend roads.