Constraint distributions in standard APO

Yes, standard Supply Network Planning (SNP) within APO can achieve this, although a lot of thought needs to go into the design and set-up of the system and data. The main aspect of achieving the single distribution plan would be to have one APO instance that connects with your six separate R/3 systems. Within SNP, one option would be to use Capable to Match (CTM) which creates a feasible multi-site solution based on the available stock, production capacities and transportation capabilities.