After Market Stereo

Hello,
 
     I was thinkin about maybe putting an after market stereo in my Jetta sometime this summer and i was just wondering how big of a pain it is. Do i have to replace the factory amp? and im pretty sure i will lose the 6 disc cd changer right? I love the monsoon sound but i wanted to put a sub in. Has anyone put an after market stereo in thier Jetta? Thanks

I don''t know about the cd changer but i know you can keep the factory amp, the wiring harness that allows you to keep it is kinda expensive. but it will work.