Well after some research I found out that the inputs on the J525 unit are coming from the Concert head Unit. this head unit outputs 4x20 Watt.
The speakers are powered by the J525 which is sitting in the left side of the trunk, behind the left rear wheel.
I think I need some sort of amp between the laptop audio output and the J525 unit. any ideas?
Additional info: the output from the Concert Head Unit is Low Level !!