ive got a wiring diagram from toyota for a 96 ES300 now and from looking at it, i cant see why it cannot be used... im just a little confused over a few things on it...
coming out of the head unit on plug A is: (plug B is all changer control stuff)
RR
RL
BEEP
GND
FR
FL
MUTE
GND
ACC
AMP
B
ANT
all that comes out of the amp is the speakers, same as a normal amplifier
from my knowledge of sound systems, the factory amp should be able to be used... as long as the wiring is all figured out proply... the head unit cant be THAT much different from a aftermarket one, same as the amp, they all work the same way, its just wiring that differs