Does the stock stereo on a '02 GT2 have an external amp, or is the amplification done in the head unit?

I have a passive (un-amp'd) head unit I'd like to use instead of the stock one, but I'm not really interested in doing a ton mods to get it to work. I was hoping to use the stock wiring and speakers.

 

No amp, just radio power in a GT2 and GT3. Should be a simple install
job.

 

A small amp with some new speakers will sound ALOT better with the headunit.
The stock speakers are NOKIAs

 

Have you done the upgrade....not that you can hear much of the music while moving but this system is a disgrace. Any suggestions or experience how to best improve on the stereo without adding any weight.