Chiptuning and extra tuning box, what happens?

Hi forum, don’t worry, I don’t have to try this configuration and don’t want to turn 5 tuning boxes in series to achieve six times the power I’m only interested in what happens once when you equip a vehicle with a chip tuning (chip tuning software on the engine control unit) and then a so-called tuning box “before” this engine control unit jams? Does it cause error messages? Does the power increase pick up? What do you think? VG Tom