Actually the cabs being different is the least of you worries in a common bus wiring. It is the dual cab which can be problematic. If all 3 cabs (power packs) were single (and even different brands) units, that would not matter at all. But you need to find out the internal wiring of that dual cab. They might already have a common wired internally. If you then make the other output the common, you will cause a short.
But if each output of the dual cabs is totally isolated from the other (as if each was a separate unit) then you can use the common bus circuit you found (and a single pole cab selector).
