1995 XJ6 cd player
 

Question if i have cable in rear deck for a cd player so if i buy cd player oem will it like plug and play also radio sounds bad speakers are good ?

Best place for this would be the x300 forum :P

However as a bit of an audio nut I can take a pretty good guess why the speakers sound bad. Either the surround of the speakers has disintegrated leaving the Cone flapping around or the voice could have melted off (someone blew them up haha) another simple fix could be that some mad man has set the EQ (bass, mid, treble) in some bizarre fashion. I'd start there and work back to replacing the speakers.

If you push on the Cone and hear a scraping sound they are blown up.

As for the CD player, I'm sure an oem cd play for that car found fit perfect. The cable in the back could either be a remote wire (likely thin and blue) for a subwoofer or cable for a cd changer (big cable with connector)