When Dream Theater travel to certain countries, they'll take less equipment to keep the costs of transporting all of their gear down. That is their B-rig, which you'll spot by MP's smaller drumkit (with only two bass drums instead of three), and JR using one of his older, lighter keyboard stands, and a much less fancy continuum stand. The A-rig is of course their full rig that they'll use for places such as the US.