i would think the system is basically the same as is fitted in the IS Models so,
the system will be an active system,basicaly everything is controlled by the AMP,even the audio controls are if the amp is removed you will no longer be able to use the head unit.....bizzare i know.........so this is where the frequency splitter(crossover) is also located...................................and where is this you ask......i would think behind the dash,the best place to look first is the back of the glove box,after that .......i will find out
to recap,if you want to upgrade only the speakers of this system it would be better to get LLC(line level converters) plugged into the original speaker wires these signals then would be good enough to power an amp(if you use the wires dirrectly to the amp you will fry it
otherwise its better to rip the whole lot out and start afresh
mat:saint: