lx450user

I'm looking for a wiring diagram for the stereo wires ,and a link to where I can find out if I have the Mark levinsion amp and system in my suv . If I do can I use the amp ? I was told it puts out a different ohm than a regular speaker use and that I couldn't use it I need a link or info to what speaker sizes I have now . I have 1 in each door 2 in the dash and one in the center console facing forward I think its a subwoofer , I'm going to replace the stereo and all the speakers and the amp if I need to . The stereo I'm going to put in is the kenwood ddx 9903s it has 50 watts per channel so if that is enough power for regular listening I might not need a amp . Is 50 watts enough for regular listening ? Any information anyone can give me would help .