Hey,
As Lorenzo said it's as broad as it's long...
I had some recent success with sigmund~ in conjunction with William Brent's [pitchEnv~] http://williambrent.conflations.com/pages/research.html This was for a mono source only but there's no reason why you couldn't get some harmonising etc etc. in a Voyager stylee going from that.
There's also umpteen various settings and tweeks you can apply to sigmund.
As a side note I was chatting with the UoHudd hardcore-coder#1 recently who was telling me the algorithm in sigmund is about as good as it gets currently, so perhaps asking Miller to chuck something together might not be a goer:) but hey who knows.
Best wishes,
Julian