Assuming that you're trying to feed an entire building on one ATS-
Unless you go with "oil rig" connectors, I think the biggest one you'll commonly find is 400a (camlock e1016 style or equiv. single cond.), so paralleling is going to happen. Likewise, to achieve 800a, you'll need to parallel conductors anyway. I wouldn't try to use multi-conductor cable for 200a unless you have some gorillas to handle it. (You could use 200a pin/sleeve connectors with 5 single leads into them. Check to see if they're rated for it.) I'd use single conductor type SC, it's rated for this use.
Oh, also, if you're feeding multiple 200a connectors off an 800a generator, very likely you'll need OCP for each one at the generator. Not sure whether you could apply the tap rules to this, but probably not.
This is definitely something that I wouldn't send a random crew to connect. It needs someone that has been trained to do so and understands what can happen if, say, the parallel conductors are crossed at one end. (When an old friend at New England Tel (now retired) set up emergency generator connections at transmission facilities, he'd install lugs-n-studs instead of connectors. Because it was more that just plugging in, the power techs made the connections and he was much more confident that it would be correct.)
Written procedures- write up the procedure to connect and disconnect and post it everywhere, esp as the buildings are different. Building 'A' might only need two or three sets of connections, building 'B' might need six.
Be careful where the SBJ is located...