Amplifier Upgrade

[TonyP]

I'm planning to upgrade the sound system in my 2000 GS300. I found the amp behind the glove box. Can I simply disonnect the amp input from the head unit and tap-in to get pre-amp outputs to my new amp? Or is there something about the Pioneer stereos that require the stock amp to remain connected, requiring me to go with speaker level inputs (with distortion!) to the new amps? Also, does anyone know if there are adapters available to plug into the speaker wiring harness versus tapping in to each wire?