i want to replace my factory head unit with aftermarket.but there are so many out there I'm lost.

Hear is what i want to do.

i want to also add a 4 ch amp

and keep the RAP i don't care if i lose the chime feature

By the way i do have the monsoon sound system in my 2004 grand prix gt.

Or if i can keep the factor head unit and add a amp but get one with high level inputs on the amp.(i realy dont want to use a LOC)i dont care for them.

Please help