SLV300E

Waz up? well its come to the time where i want to upgrade my audio system... well get one first... Anyways I have a 1992 300E W124 chassis. In my trunk there is a male cable that reveals itself on the left rear area of the trunk, im guessing this is for the changer? Can the stock becker deck support a changer? Second of all, i want to get some new speakers and I was wondering what size i would need for the doors and for the front dash. Would I need to rewire everything or can i just connect my new speakers to the old cables that my stock speakers ran off of? well hope to hear from somone soon thanks again