Separate amp under the pass seat?

I was cleaning the car the other day and found an enclosure under the passengers seat with a part that looks like an audio amplifier. Do the cars equipped with the standard NAV headunit (non JBL) have an external amplifier or what is that part for ?

Thanks

 

Thanks for your reply. Well, it's an EU car but the JBL System is also an upgrade here. The JBL logo is missing on the headunit. Also I haven't found a subwoofer in the car (so far).

 

Ok, my car's audio setup is the one that is described as "Korea version with Nav". Seems that in Europe (at least the cars in Switzerland) with the Nav screen (non-JBL) come with a small additional amp. But this guy only powers the two front door speakers. Very strange setup, as the front dash speakers are powered directly by the HU. There is a y-junction were the same wires go into the amp. Therefore it's a high level amp that is used to provide more power to the woofers in the door. Honestly, I'm not a fan of this way Toyota added more bass

 

For further reference I have included a pic of the amp and the schematic wiring of the speakers and amp. I want to wire in a JBL MS-8 but have problems locating the L109 junction connector.