Which subwoofer do I need in the Fiat Ducato?

In Fiat Ducato III, Citroen Jumper 2, Peugeot Boxer 2 or Dodge RamProMaster SERIES 7 can be installed the UG FIAT SUB-KIT + USB 6AR subwoofer as well as the UG FIAT SUB 6A active subwoofer. For SERIES 8 vehicles is only the UG FIAT SUB 6A suitable!