The first 2 points are indeed possible
(-have a single mono analog input to be routed to both the A and B
machines ( and this is possible)
-have the stereo output of each
machine assigned respectively to specific H8000 firewire channels so to
have their signal available in the digital domain ( seen as inputs in
for the third one, everything depends on the software, as you'll be doing the routing in it.
You should simply try it.