wouldn't these methods all just produce a "unison" mono?
there's no computer dictating when each voice / envelope should trigger. midi would just make them all trigger at once.
also there is no midi thru as of yet, so you could only have the midi out of one mb go into the midi in of another. still would be a unison monophonic voice
you could theoretically send midi cables to multiple minibrutes, then perhaps use a program on a computer to handle the voicing computations, but i'm not aware of anything that works like that.
things that do chain together (phattys, mopho w/ tetra, etc) are designed with that purposes specifically in mind, and have the ability to handle the necessary computations accordingly